diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2a00d5f..3938593 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,9 +2,14 @@
 
 ## [[unpublished]](https://github.com/mlange-42/arche-model/compare/v0.7.0...main)
 
+### Features
+
+* Adds `reporter.Callback` for direct retrieval of observer output in Go code (#61)
+
 ### Bugfixes
 
 * Fix typo in error message when adding UI system as normal system (#60)
+* Fix reporters did not work with unspecified `UpdateInterval` (#61)
 
 ## [[v0.7.0]](https://github.com/mlange-42/arche-model/compare/v0.6.0...v0.7.0)
 
diff --git a/reporter/callback.go b/reporter/callback.go
new file mode 100644
index 0000000..cd64637
--- /dev/null
+++ b/reporter/callback.go
@@ -0,0 +1,40 @@
+package reporter
+
+import (
+	"github.com/mlange-42/arche-model/observer"
+	"github.com/mlange-42/arche/ecs"
+)
+
+// Callback reporter calling a function on each update.
+type Callback struct {
+	Observer       observer.Row // Observer to get data from.
+	UpdateInterval int          // Update/print interval in model ticks.
+	HeaderCallback func(header []string)
+	Callback       func(step int, row []float64)
+	step           int64
+}
+
+// Initialize the system
+func (s *Callback) Initialize(w *ecs.World) {
+	s.Observer.Initialize(w)
+	if s.UpdateInterval == 0 {
+		s.UpdateInterval = 1
+	}
+	if s.HeaderCallback != nil {
+		s.HeaderCallback(s.Observer.Header())
+	}
+	s.step = 0
+}
+
+// Update the system
+func (s *Callback) Update(w *ecs.World) {
+	s.Observer.Update(w)
+	if s.step%int64(s.UpdateInterval) == 0 {
+		values := s.Observer.Values(w)
+		s.Callback(int(s.step), values)
+	}
+	s.step++
+}
+
+// Finalize the system
+func (s *Callback) Finalize(w *ecs.World) {}
diff --git a/reporter/callback_test.go b/reporter/callback_test.go
new file mode 100644
index 0000000..728949d
--- /dev/null
+++ b/reporter/callback_test.go
@@ -0,0 +1,35 @@
+package reporter_test
+
+import (
+	"fmt"
+
+	"github.com/mlange-42/arche-model/model"
+	"github.com/mlange-42/arche-model/reporter"
+	"github.com/mlange-42/arche-model/system"
+)
+
+func ExampleCallback() {
+	// Create a new model.
+	m := model.New()
+
+	data := [][]float64{}
+
+	// Add a Print reporter with an Observer.
+	m.AddSystem(&reporter.Callback{
+		Observer: &ExampleObserver{},
+		Callback: func(step int, row []float64) {
+			data = append(data, row)
+		},
+		HeaderCallback: func(header []string) {},
+	})
+
+	// Add a termination system that ends the simulation.
+	m.AddSystem(&system.FixedTermination{Steps: 3})
+
+	// Run the simulation.
+	m.Run()
+
+	fmt.Println(data)
+	// Output:
+	// [[1 2 3] [1 2 3] [1 2 3]]
+}
diff --git a/reporter/csv.go b/reporter/csv.go
index d5481df..77d71b6 100644
--- a/reporter/csv.go
+++ b/reporter/csv.go
@@ -28,6 +28,9 @@ type CSV struct {
 func (s *CSV) Initialize(w *ecs.World) {
 	s.Observer.Initialize(w)
 	s.header = s.Observer.Header()
+	if s.UpdateInterval == 0 {
+		s.UpdateInterval = 1
+	}
 	if s.Sep == "" {
 		s.Sep = ","
 	}
diff --git a/reporter/csv_example_test.go b/reporter/csv_example_test.go
index ef7f0ce..8bb822a 100644
--- a/reporter/csv_example_test.go
+++ b/reporter/csv_example_test.go
@@ -13,10 +13,9 @@ func ExampleCSV() {
 
 	// Add a CSV reporter with an Observer.
 	m.AddSystem(&reporter.CSV{
-		Observer:       &ExampleObserver{},
-		File:           "../out/test.csv",
-		Sep:            ";",
-		UpdateInterval: 10,
+		Observer: &ExampleObserver{},
+		File:     "../out/test.csv",
+		Sep:      ";",
 	})
 
 	// Add a termination system that ends the simulation.
diff --git a/reporter/csv_snaphot.go b/reporter/csv_snaphot.go
index ac23181..a2c0487 100644
--- a/reporter/csv_snaphot.go
+++ b/reporter/csv_snaphot.go
@@ -27,6 +27,9 @@ type SnapshotCSV struct {
 func (s *SnapshotCSV) Initialize(w *ecs.World) {
 	s.Observer.Initialize(w)
 	s.header = s.Observer.Header()
+	if s.UpdateInterval == 0 {
+		s.UpdateInterval = 1
+	}
 
 	if s.Sep == "" {
 		s.Sep = ","
diff --git a/reporter/csv_snapshot_example_test.go b/reporter/csv_snapshot_example_test.go
index 25159d4..bd0be56 100644
--- a/reporter/csv_snapshot_example_test.go
+++ b/reporter/csv_snapshot_example_test.go
@@ -13,10 +13,9 @@ func ExampleSnapshotCSV() {
 
 	// Add a SnapshotCSV reporter with an Observer.
 	m.AddSystem(&reporter.SnapshotCSV{
-		Observer:       &ExampleSnapshotObserver{},
-		FilePattern:    "../out/test-%06d.csv",
-		Sep:            ";",
-		UpdateInterval: 10,
+		Observer:    &ExampleSnapshotObserver{},
+		FilePattern: "../out/test-%06d.csv",
+		Sep:         ";",
 	})
 
 	// Add a termination system that ends the simulation.
diff --git a/reporter/csv_snapshot_test.go b/reporter/csv_snapshot_test.go
index 786e38f..91ed4ef 100644
--- a/reporter/csv_snapshot_test.go
+++ b/reporter/csv_snapshot_test.go
@@ -14,9 +14,8 @@ func TestSnapshotCSV(t *testing.T) {
 	m := model.New()
 
 	m.AddSystem(&reporter.SnapshotCSV{
-		Observer:       &ExampleSnapshotObserver{},
-		FilePattern:    "../out/test-%06d.csv",
-		UpdateInterval: 10,
+		Observer:    &ExampleSnapshotObserver{},
+		FilePattern: "../out/test-%06d.csv",
 	})
 	m.AddSystem(&system.FixedTermination{Steps: 100})
 
diff --git a/reporter/csv_test.go b/reporter/csv_test.go
index d675b72..5e6245d 100644
--- a/reporter/csv_test.go
+++ b/reporter/csv_test.go
@@ -14,9 +14,8 @@ func TestCSV(t *testing.T) {
 	m := model.New()
 
 	m.AddSystem(&reporter.CSV{
-		Observer:       &ExampleObserver{},
-		File:           "../out/test.csv",
-		UpdateInterval: 10,
+		Observer: &ExampleObserver{},
+		File:     "../out/test.csv",
 	})
 	m.AddSystem(&system.FixedTermination{Steps: 100})
 
diff --git a/reporter/print.go b/reporter/print.go
index 4229a46..5a5ee34 100644
--- a/reporter/print.go
+++ b/reporter/print.go
@@ -19,6 +19,9 @@ type Print struct {
 func (s *Print) Initialize(w *ecs.World) {
 	s.Observer.Initialize(w)
 	s.header = s.Observer.Header()
+	if s.UpdateInterval == 0 {
+		s.UpdateInterval = 1
+	}
 	s.step = 0
 }
 
diff --git a/reporter/print_test.go b/reporter/print_test.go
index 67d2f63..53e9ef1 100644
--- a/reporter/print_test.go
+++ b/reporter/print_test.go
@@ -12,12 +12,11 @@ func ExamplePrint() {
 
 	// Add a Print reporter with an Observer.
 	m.AddSystem(&reporter.Print{
-		Observer:       &ExampleObserver{},
-		UpdateInterval: 10,
+		Observer: &ExampleObserver{},
 	})
 
 	// Add a termination system that ends the simulation.
-	m.AddSystem(&system.FixedTermination{Steps: 20})
+	m.AddSystem(&system.FixedTermination{Steps: 3})
 
 	// Run the simulation.
 	m.Run()
@@ -26,4 +25,6 @@ func ExamplePrint() {
 	// [1 2 3]
 	// [A B C]
 	// [1 2 3]
+	// [A B C]
+	// [1 2 3]
 }