diff --git a/kmath-histograms/src/commonMain/kotlin/space/kscience/kmath/histogram/UniformHistogram1D.kt b/kmath-histograms/src/commonMain/kotlin/space/kscience/kmath/histogram/UniformHistogram1D.kt
index e2811602c..758e7969a 100644
--- a/kmath-histograms/src/commonMain/kotlin/space/kscience/kmath/histogram/UniformHistogram1D.kt
+++ b/kmath-histograms/src/commonMain/kotlin/space/kscience/kmath/histogram/UniformHistogram1D.kt
@@ -37,37 +37,53 @@ public class UniformHistogram1D<V : Any>(
     }
 }
 
+/**
+ * An algebra for uniform histograms in 1D real space
+ */
 public class UniformHistogram1DGroup<V : Any, A>(
     public val valueAlgebra: A,
     public val binSize: Double,
     public val startPoint: Double = 0.0,
-) : Group<UniformHistogram1D<V>>, ScaleOperations<UniformHistogram1D<V>> where A : Ring<V>, A : ScaleOperations<V> {
+) : Group<Histogram1D<Double, V>>, ScaleOperations<Histogram1D<Double, V>> where A : Ring<V>, A : ScaleOperations<V> {
+
     override val zero: UniformHistogram1D<V> by lazy { UniformHistogram1D(this, emptyMap()) }
 
-    public fun getIndex(at: Double): Int = floor((at - startPoint) / binSize).toInt()
+    /**
+     * Get index of a bin
+     */
+    @PublishedApi
+    internal fun getIndex(at: Double): Int = floor((at - startPoint) / binSize).toInt()
 
-    override fun add(left: UniformHistogram1D<V>, right: UniformHistogram1D<V>): UniformHistogram1D<V> = valueAlgebra {
-        require(left.group == this@UniformHistogram1DGroup)
-        require(right.group == this@UniformHistogram1DGroup)
-        val keys = left.values.keys + right.values.keys
+    override fun add(
+        left: Histogram1D<Double, V>,
+        right: Histogram1D<Double, V>,
+    ): UniformHistogram1D<V> = valueAlgebra {
+        val leftUniform = produceFrom(left)
+        val rightUniform = produceFrom(right)
+        val keys = leftUniform.values.keys + rightUniform.values.keys
         UniformHistogram1D(
             this@UniformHistogram1DGroup,
-            keys.associateWith { (left.values[it] ?: valueAlgebra.zero) + (right.values[it] ?: valueAlgebra.zero) }
+            keys.associateWith {
+                (leftUniform.values[it] ?: valueAlgebra.zero) + (rightUniform.values[it] ?: valueAlgebra.zero)
+            }
         )
     }
 
-    override fun UniformHistogram1D<V>.unaryMinus(): UniformHistogram1D<V> = valueAlgebra {
-        UniformHistogram1D(this@UniformHistogram1DGroup, values.mapValues { -it.value })
+    override fun Histogram1D<Double, V>.unaryMinus(): UniformHistogram1D<V> = valueAlgebra {
+        UniformHistogram1D(this@UniformHistogram1DGroup, produceFrom(this@unaryMinus).values.mapValues { -it.value })
     }
 
     override fun scale(
-        a: UniformHistogram1D<V>,
+        a: Histogram1D<Double, V>,
         value: Double,
     ): UniformHistogram1D<V> = UniformHistogram1D(
         this@UniformHistogram1DGroup,
-        a.values.mapValues { valueAlgebra.scale(it.value, value) }
+        produceFrom(a).values.mapValues { valueAlgebra.scale(it.value, value) }
     )
 
+    /**
+     *
+     */
     public inline fun produce(block: Histogram1DBuilder<Double, V>.() -> Unit): UniformHistogram1D<V> {
         val map = HashMap<Int, V>()
         val builder = object : Histogram1DBuilder<Double, V> {
@@ -87,7 +103,7 @@ public class UniformHistogram1DGroup<V : Any, A>(
      * is increased by one. If not, all bins including values from this bin are increased by fraction
      * (conserving the norming).
      */
-    @UnstableKMathAPI
+    @OptIn(UnstableKMathAPI::class)
     public fun produceFrom(histogram: Histogram1D<Double, V>): UniformHistogram1D<V> =
         if ((histogram as? UniformHistogram1D)?.group == this) histogram
         else {
diff --git a/kmath-histograms/src/commonTest/kotlin/space/kscience/kmath/histogram/UniformHistogram1DTest.kt b/kmath-histograms/src/commonTest/kotlin/space/kscience/kmath/histogram/UniformHistogram1DTest.kt
index 8d5cb8fb1..09bf3939d 100644
--- a/kmath-histograms/src/commonTest/kotlin/space/kscience/kmath/histogram/UniformHistogram1DTest.kt
+++ b/kmath-histograms/src/commonTest/kotlin/space/kscience/kmath/histogram/UniformHistogram1DTest.kt
@@ -34,9 +34,17 @@ internal class UniformHistogram1DTest {
     }
 
     @Test
-    fun rebin() = runTest {
-        val h1 = Histogram.uniform1D(DoubleField, 0.1).produce(generator.nextDoubleBuffer(10000))
-        val h2 = Histogram.uniform1D(DoubleField,0.3).produceFrom(h1)
+    fun rebinDown() = runTest {
+        val h1 = Histogram.uniform1D(DoubleField, 0.01).produce(generator.nextDoubleBuffer(10000))
+        val h2 = Histogram.uniform1D(DoubleField,0.03).produceFrom(h1)
+
+        assertEquals(10000, h2.bins.sumOf { it.binValue }.toInt())
+    }
+
+    @Test
+    fun rebinUp() = runTest {
+        val h1 = Histogram.uniform1D(DoubleField, 0.03).produce(generator.nextDoubleBuffer(10000))
+        val h2 = Histogram.uniform1D(DoubleField,0.01).produceFrom(h1)
 
         assertEquals(10000, h2.bins.sumOf { it.binValue }.toInt())
     }