diff --git a/README.md b/README.md
index 56de831..c085756 100644
--- a/README.md
+++ b/README.md
@@ -6,8 +6,8 @@ MCResourceAnalyzer gathers data from Minecraft region files to determine the emp
 
 1. Clone the repository and build it with Maven or [download the latest release here](https://github.com/Meeples10/MCResourceAnalyzer/releases).
 2. If your world was generated with a version after Beta 1.3, use the `region` directory from your Minecraft world as the program's input.
-If the world was generated with a version between Infdev 20100327 and Beta 1.2, use the entire world directory to `region` as the program's input.
-If the world was generated with Indev, rename the save file to `world.mclevel` and copy it to the same directory as the program.
+If the world was generated with a version between Infdev 20100327 and Beta 1.2, use the entire world directory as the input.
+If the world was generated with Indev, use the `world.mclevel` file as the input.
 3. Run the program with `java -jar mc-resource-analyzer-x.x.x.jar [options...] [input path]`. After analyzing the world, the program will create a file in the same directory named `data.csv`.
 
 Note that the numbers for `minecraft:air` may be inaccurate at high Y values due to the way Minecraft stores chunks.
@@ -46,7 +46,7 @@ java -jar mc-resource-analyzer-x.x.x.jar [-hHmsStV] [-B=PATH] [-M=PATH] [-o=STRI
 
 ### Version compatibility
 
-MCResourceAnalyzer 1.2.0 can analyze worlds generated with any version of Minecraft: Java Edition between Indev 0.31 20100122 and 1.20.1.
+MCResourceAnalyzer 1.2.1 can analyze worlds generated with any version of Minecraft: Java Edition between Indev 0.31 20100122 and 1.20.1.
 
 Note that Indev worlds with the `Long` and `Deep` world shapes are not supported.
 
diff --git a/pom.xml b/pom.xml
index 7f43e3e..001891f 100644
--- a/pom.xml
+++ b/pom.xml
@@ -3,7 +3,7 @@
 
     <groupId>io.github.meeples10.mcresourceanalyzer</groupId>
     <artifactId>mc-resource-analyzer</artifactId>
-    <version>1.2.0</version>
+    <version>1.2.1</version>
     <packaging>jar</packaging>
 
     <name>MCResourceAnalyzer</name>
diff --git a/src/main/java/io/github/meeples10/mcresourceanalyzer/Analysis.java b/src/main/java/io/github/meeples10/mcresourceanalyzer/Analysis.java
index caf66d0..78f6848 100644
--- a/src/main/java/io/github/meeples10/mcresourceanalyzer/Analysis.java
+++ b/src/main/java/io/github/meeples10/mcresourceanalyzer/Analysis.java
@@ -1,9 +1,9 @@
 package io.github.meeples10.mcresourceanalyzer;
 
-import java.util.HashMap;
+import java.util.Hashtable;
 import java.util.Map;
 
 public class Analysis {
-    public Map<String, Long> blocks = new HashMap<String, Long>();
-    public Map<String, HashMap<Integer, Long>> heights = new HashMap<String, HashMap<Integer, Long>>();
+    public Map<String, Long> blocks = new Hashtable<>();
+    public Map<String, Hashtable<Integer, Long>> heights = new Hashtable<>();
 }
diff --git a/src/main/java/io/github/meeples10/mcresourceanalyzer/AnalyzerThread.java b/src/main/java/io/github/meeples10/mcresourceanalyzer/AnalyzerThread.java
index af89c6f..8201d4d 100644
--- a/src/main/java/io/github/meeples10/mcresourceanalyzer/AnalyzerThread.java
+++ b/src/main/java/io/github/meeples10/mcresourceanalyzer/AnalyzerThread.java
@@ -1,16 +1,52 @@
 package io.github.meeples10.mcresourceanalyzer;
 
 import java.util.HashSet;
+import java.util.Hashtable;
 import java.util.Set;
 
 public abstract class AnalyzerThread extends Thread {
+    final RegionAnalyzer ra;
     final Region r;
     final Set<Analysis> analyses = new HashSet<>();
 
-    public AnalyzerThread(Region region) {
+    public AnalyzerThread(RegionAnalyzer ra, Region region) {
+        this.ra = ra;
         r = region;
         setName(r.name);
     }
 
-    public abstract void run();
+    public void run() {
+        process();
+        ra.add(combineAnalyses());
+    }
+
+    public abstract void process();
+
+    private Analysis combineAnalyses() {
+        Analysis out = new Analysis();
+        for(Analysis a : analyses) {
+            for(String blockName : a.blocks.keySet()) {
+                long count = a.blocks.get(blockName);
+                if(out.blocks.containsKey(blockName)) {
+                    out.blocks.put(blockName, out.blocks.get(blockName) + count);
+                } else {
+                    out.blocks.put(blockName, count);
+                }
+            }
+            for(String blockName : a.heights.keySet()) {
+                if(!out.heights.containsKey(blockName)) {
+                    out.heights.put(blockName, new Hashtable<Integer, Long>());
+                }
+                for(int y : a.heights.get(blockName).keySet()) {
+                    long count = a.heights.get(blockName).get(y);
+                    if(out.heights.get(blockName).containsKey(y)) {
+                        out.heights.get(blockName).put(y, out.heights.get(blockName).get(y) + count);
+                    } else {
+                        out.heights.get(blockName).put(y, count);
+                    }
+                }
+            }
+        }
+        return out;
+    }
 }
diff --git a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzer.java b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzer.java
index 103a73b..0f35a4d 100644
--- a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzer.java
+++ b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzer.java
@@ -4,8 +4,8 @@
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Comparator;
-import java.util.HashMap;
 import java.util.HashSet;
+import java.util.Hashtable;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -19,8 +19,8 @@
 public abstract class RegionAnalyzer {
     private Version version;
     public int chunkCount = 0;
-    public Map<String, Long> blockCounter = new HashMap<String, Long>();
-    public Map<String, HashMap<Integer, Long>> heightCounter = new HashMap<String, HashMap<Integer, Long>>();
+    public Map<String, Long> blockCounter = new Hashtable<>();
+    public Map<String, Hashtable<Integer, Long>> heightCounter = new Hashtable<>();
     private long firstStartTime;
     public long duration;
     List<Region> regions = new ArrayList<>();
@@ -56,29 +56,12 @@ public void run(File input) {
                 pool.submit(t);
             }
             pool.shutdown();
+            threads.clear();
             try {
                 pool.awaitTermination(100, TimeUnit.DAYS);
             } catch(InterruptedException e) {
                 e.printStackTrace();
             }
-            for(AnalyzerThread t : threads) {
-                for(Analysis a : t.analyses) {
-                    for(String s : a.blocks.keySet()) {
-                        blockCounter.put(s, blockCounter.getOrDefault(s, 0L) + a.blocks.get(s));
-                    }
-                    for(String s : a.heights.keySet()) {
-                        if(heightCounter.containsKey(s)) {
-                            Map<Integer, Long> existing = heightCounter.get(s);
-                            Map<Integer, Long> heights = a.heights.get(s);
-                            for(int i : heights.keySet()) {
-                                existing.put(i, existing.getOrDefault(i, 0L) + heights.get(i));
-                            }
-                        } else {
-                            heightCounter.put(s, a.heights.get(s));
-                        }
-                    }
-                }
-            }
         }
 
         duration = System.currentTimeMillis() - getStartTime();
@@ -195,7 +178,7 @@ public String generateTable(double totalBlocks, double totalExcludingAir) {
             data.append("<table>\n");
         }
         data.append("<tr><th>id</th><th>");
-        for(int i = minY; i < maxY; i++) {
+        for(int i = minY; i <= maxY; i++) {
             data.append(i);
             data.append("</th><th>");
         }
@@ -209,7 +192,7 @@ public String generateTable(double totalBlocks, double totalExcludingAir) {
             data.append("<td>");
             data.append(Main.modernizeIDs ? Main.getStringID(key) : key);
             data.append("</td>");
-            for(int i = minY; i < maxY; i++) {
+            for(int i = minY; i <= maxY; i++) {
                 if(!heightCounter.get(key).containsKey(i)) {
                     data.append("<td>0</td>");
                 } else {
@@ -256,7 +239,7 @@ static boolean mergeStates(byte id) {
     static void airHack(Analysis a, int sectionY, String airID) {
         if(Main.allowHack && sectionY < 15) {
             if(!a.blocks.containsKey(airID)) a.blocks.put(airID, 0L);
-            if(!a.heights.containsKey(airID)) a.heights.put(airID, new HashMap<Integer, Long>());
+            if(!a.heights.containsKey(airID)) a.heights.put(airID, new Hashtable<Integer, Long>());
             for(; sectionY < 16; sectionY++) {
                 a.blocks.put(airID, a.blocks.get(airID) + 4096L);
                 for(int y = sectionY * 16; y < sectionY * 16 + 16; y++) {
@@ -270,7 +253,7 @@ static void airHack(Analysis a, int sectionY, String airID) {
         }
     }
 
-    int getMinimumY() {
+    private int getMinimumY() {
         int min = Integer.MAX_VALUE;
         for(Map<Integer, Long> map : heightCounter.values()) {
             for(int i : map.keySet()) {
@@ -286,7 +269,7 @@ int getMinimumY() {
         }
     }
 
-    int getMaximumY() {
+    private int getMaximumY() {
         int max = Integer.MIN_VALUE;
         for(Map<Integer, Long> map : heightCounter.values()) {
             for(int i : map.keySet()) {
@@ -296,12 +279,29 @@ int getMaximumY() {
             }
         }
         if(version == Version.INDEV || version == Version.ALPHA || version == Version.MCREGION) {
-            return 128;
+            return 127;
         } else {
             return max > 255 ? max : 255;
         }
     }
 
+    synchronized void add(Analysis a) {
+        for(String s : a.blocks.keySet()) {
+            blockCounter.put(s, blockCounter.getOrDefault(s, 0L) + a.blocks.get(s));
+        }
+        for(String s : a.heights.keySet()) {
+            if(heightCounter.containsKey(s)) {
+                Map<Integer, Long> existing = heightCounter.get(s);
+                Map<Integer, Long> heights = a.heights.get(s);
+                for(int i : heights.keySet()) {
+                    existing.put(i, existing.getOrDefault(i, 0L) + heights.get(i));
+                }
+            } else {
+                heightCounter.put(s, a.heights.get(s));
+            }
+        }
+    }
+
     public enum Version {
         ANVIL_118(RegionAnalyzerAnvil118.class, true),
         ANVIL_2021(RegionAnalyzerAnvil2021.class, true),
diff --git a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAlpha.java b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAlpha.java
index 3293e9c..e601b8c 100644
--- a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAlpha.java
+++ b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAlpha.java
@@ -3,7 +3,7 @@
 import java.io.File;
 import java.io.FileInputStream;
 import java.util.ArrayList;
-import java.util.HashMap;
+import java.util.Hashtable;
 import java.util.List;
 
 import net.minecraft.nbt.CompressedStreamTools;
@@ -89,7 +89,7 @@ private void analyzeChunk(byte[] blocks, byte[] data) {
                         a.blocks.put(blockName, 1L);
                     }
                     if(!a.heights.containsKey(blockName)) {
-                        a.heights.put(blockName, new HashMap<Integer, Long>());
+                        a.heights.put(blockName, new Hashtable<Integer, Long>());
                     }
                     if(a.heights.get(blockName).containsKey(y)) {
                         a.heights.get(blockName).put(y, a.heights.get(blockName).get(y) + 1L);
diff --git a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil118.java b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil118.java
index f27c7c8..7071684 100644
--- a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil118.java
+++ b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil118.java
@@ -3,7 +3,7 @@
 import java.io.DataInputStream;
 import java.io.File;
 import java.io.IOException;
-import java.util.HashMap;
+import java.util.Hashtable;
 
 import net.minecraft.nbt.CompressedStreamTools;
 import net.minecraft.nbt.NBTTagCompound;
@@ -40,9 +40,8 @@ public void findChunks(File regionDir) {
     @Override
     public void analyze() {
         for(Region r : regions) {
-            threads.add(new AnalyzerThread(r) {
-                @Override
-                public void run() {
+            threads.add(new AnalyzerThread(this, r) {
+                public void process() {
                     for(Chunk c : r.chunks) {
                         try {
                             Analysis a = processRegion(r.file, c.x(), c.z());
@@ -98,7 +97,7 @@ private Analysis analyzeChunk(NBTTagList sections) {
                             a.blocks.put(blockName, 1L);
                         }
                         if(!a.heights.containsKey(blockName)) {
-                            a.heights.put(blockName, new HashMap<Integer, Long>());
+                            a.heights.put(blockName, new Hashtable<Integer, Long>());
                         }
                         if(a.heights.get(blockName).containsKey(actualY)) {
                             a.heights.get(blockName).put(actualY, a.heights.get(blockName).get(actualY) + 1L);
diff --git a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil2012.java b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil2012.java
index 58e1d45..da68f0b 100644
--- a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil2012.java
+++ b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil2012.java
@@ -3,7 +3,7 @@
 import java.io.DataInputStream;
 import java.io.File;
 import java.io.IOException;
-import java.util.HashMap;
+import java.util.Hashtable;
 
 import net.minecraft.nbt.CompressedStreamTools;
 import net.minecraft.nbt.NBTTagCompound;
@@ -39,9 +39,8 @@ public void findChunks(File regionDir) {
     @Override
     public void analyze() {
         for(Region r : regions) {
-            threads.add(new AnalyzerThread(r) {
-                @Override
-                public void run() {
+            threads.add(new AnalyzerThread(this, r) {
+                public void process() {
                     for(Chunk c : r.chunks) {
                         try {
                             Analysis a = processRegion(r.file, c.x(), c.z());
@@ -107,7 +106,7 @@ private Analysis analyzeChunk(NBTTagList sections) {
                             a.blocks.put(blockName, 1L);
                         }
                         if(!a.heights.containsKey(blockName)) {
-                            a.heights.put(blockName, new HashMap<Integer, Long>());
+                            a.heights.put(blockName, new Hashtable<Integer, Long>());
                         }
                         if(a.heights.get(blockName).containsKey(actualY)) {
                             a.heights.get(blockName).put(actualY, a.heights.get(blockName).get(actualY) + 1L);
diff --git a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil2018.java b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil2018.java
index badfc2a..dfcb9e7 100644
--- a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil2018.java
+++ b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil2018.java
@@ -3,7 +3,7 @@
 import java.io.DataInputStream;
 import java.io.File;
 import java.io.IOException;
-import java.util.HashMap;
+import java.util.Hashtable;
 
 import net.minecraft.nbt.CompressedStreamTools;
 import net.minecraft.nbt.NBTTagCompound;
@@ -42,9 +42,8 @@ public void analyze() {
         // The air hack does not seem to work for this version
         Main.allowHack = false;
         for(Region r : regions) {
-            threads.add(new AnalyzerThread(r) {
-                @Override
-                public void run() {
+            threads.add(new AnalyzerThread(this, r) {
+                public void process() {
                     for(Chunk c : r.chunks) {
                         try {
                             Analysis a = processRegion(r.file, c.x(), c.z());
@@ -100,7 +99,7 @@ private Analysis analyzeChunk(NBTTagList sections) {
                             a.blocks.put(blockName, 1L);
                         }
                         if(!a.heights.containsKey(blockName)) {
-                            a.heights.put(blockName, new HashMap<Integer, Long>());
+                            a.heights.put(blockName, new Hashtable<Integer, Long>());
                         }
                         if(a.heights.get(blockName).containsKey(actualY)) {
                             a.heights.get(blockName).put(actualY, a.heights.get(blockName).get(actualY) + 1L);
diff --git a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil2021.java b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil2021.java
index cc34573..8ebb560 100644
--- a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil2021.java
+++ b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerAnvil2021.java
@@ -3,7 +3,7 @@
 import java.io.DataInputStream;
 import java.io.File;
 import java.io.IOException;
-import java.util.HashMap;
+import java.util.Hashtable;
 
 import net.minecraft.nbt.CompressedStreamTools;
 import net.minecraft.nbt.NBTTagCompound;
@@ -40,9 +40,8 @@ public void findChunks(File regionDir) {
     @Override
     public void analyze() {
         for(Region r : regions) {
-            threads.add(new AnalyzerThread(r) {
-                @Override
-                public void run() {
+            threads.add(new AnalyzerThread(this, r) {
+                public void process() {
                     for(Chunk c : r.chunks) {
                         try {
                             Analysis a = processRegion(r.file, c.x(), c.z());
@@ -98,7 +97,7 @@ private Analysis analyzeChunk(NBTTagList sections) {
                             a.blocks.put(blockName, 1L);
                         }
                         if(!a.heights.containsKey(blockName)) {
-                            a.heights.put(blockName, new HashMap<Integer, Long>());
+                            a.heights.put(blockName, new Hashtable<Integer, Long>());
                         }
                         if(a.heights.get(blockName).containsKey(actualY)) {
                             a.heights.get(blockName).put(actualY, a.heights.get(blockName).get(actualY) + 1L);
diff --git a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerIndev.java b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerIndev.java
index 38172a8..f59ce92 100644
--- a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerIndev.java
+++ b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerIndev.java
@@ -3,7 +3,7 @@
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.IOException;
-import java.util.HashMap;
+import java.util.Hashtable;
 
 import net.minecraft.nbt.CompressedStreamTools;
 import net.minecraft.nbt.NBTTagCompound;
@@ -72,7 +72,7 @@ private Analysis analyzeWorld(byte[] blocks, byte[] data, int width, int height)
                         a.blocks.put(blockName, 1L);
                     }
                     if(!a.heights.containsKey(blockName)) {
-                        a.heights.put(blockName, new HashMap<Integer, Long>());
+                        a.heights.put(blockName, new Hashtable<Integer, Long>());
                     }
                     if(a.heights.get(blockName).containsKey(y)) {
                         a.heights.get(blockName).put(y, a.heights.get(blockName).get(y) + 1L);
diff --git a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerMCRegion.java b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerMCRegion.java
index 501acac..16e8a67 100644
--- a/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerMCRegion.java
+++ b/src/main/java/io/github/meeples10/mcresourceanalyzer/RegionAnalyzerMCRegion.java
@@ -3,7 +3,7 @@
 import java.io.DataInputStream;
 import java.io.File;
 import java.io.IOException;
-import java.util.HashMap;
+import java.util.Hashtable;
 
 import net.minecraft.nbt.CompressedStreamTools;
 import net.minecraft.nbt.NBTTagCompound;
@@ -34,9 +34,8 @@ public void findChunks(File regionDir) {
     @Override
     public void analyze() {
         for(Region r : regions) {
-            threads.add(new AnalyzerThread(r) {
-                @Override
-                public void run() {
+            threads.add(new AnalyzerThread(this, r) {
+                public void process() {
                     for(Chunk c : r.chunks) {
                         try {
                             Analysis a = processRegion(r.file, c.x(), c.z());
@@ -95,7 +94,7 @@ private Analysis analyzeChunk(byte[] blocks, byte[] data) {
                         a.blocks.put(blockName, 1L);
                     }
                     if(!a.heights.containsKey(blockName)) {
-                        a.heights.put(blockName, new HashMap<Integer, Long>());
+                        a.heights.put(blockName, new Hashtable<Integer, Long>());
                     }
                     if(a.heights.get(blockName).containsKey(y)) {
                         a.heights.get(blockName).put(y, a.heights.get(blockName).get(y) + 1L);