diff --git a/js/common/model/RAPRatioTuple.ts b/js/common/model/RAPRatioTuple.ts
index 1da403f0..0e810b3d 100644
--- a/js/common/model/RAPRatioTuple.ts
+++ b/js/common/model/RAPRatioTuple.ts
@@ -44,6 +44,10 @@ class RAPRatioTuple {
     return new RAPRatioTuple( this.antecedent, consequent );
   }
 
+  withValueForTerm( value: number, ratioTerm: RatioTerm ): RAPRatioTuple {
+    return this.copy().setForTerm( value, ratioTerm );
+  }
+
   plusAntecedent( antecedentDelta: number ): RAPRatioTuple {
     return new RAPRatioTuple( this.antecedent + antecedentDelta, this.consequent );
   }
@@ -87,6 +91,20 @@ class RAPRatioTuple {
     }
   }
 
+  setForTerm( value: number, ratioTerm: RatioTerm ): this {
+    switch( ratioTerm ) {
+      case RatioTerm.ANTECEDENT:
+        this.antecedent = value;
+        break;
+      case RatioTerm.CONSEQUENT:
+        this.consequent = value;
+        break;
+      default:
+        assert && assert( false, `unexpected ratioTerm ${ratioTerm}` );
+    }
+    return this;
+  }
+
   copy(): RAPRatioTuple {
     return new RAPRatioTuple( this.antecedent, this.consequent );
   }
diff --git a/js/common/view/BothHandsInteractionListener.ts b/js/common/view/BothHandsInteractionListener.ts
index 006e0e00..82ec59d0 100644
--- a/js/common/view/BothHandsInteractionListener.ts
+++ b/js/common/view/BothHandsInteractionListener.ts
@@ -119,13 +119,13 @@ class BothHandsInteractionListener {
 
   /**
    * Consistently handle changing the ratio from increment/decrement
-   * @param tupleField - what field of the RAPRatioTuple are we changing
+   * @param ratioTerm - what field of the RAPRatioTuple are we changing
    * @param inputMapper - see getKeyboardInputSnappingMapper
    * @param increment - if the value is being incremented, as opposed to decremented.
    */
-  private onValueIncrementDecrement( tupleField: 'antecedent' | 'consequent', inputMapper: KeyboardInputMapper, increment: boolean ): void {
+  private onValueIncrementDecrement( ratioTerm: RatioTerm, inputMapper: KeyboardInputMapper, increment: boolean ): void {
     this.isBeingInteractedWithProperty.value = true;
-    const currentValueFromTuple = this.ratioTupleProperty.value[ tupleField ];
+    const currentValueFromTuple = this.ratioTupleProperty.value.getForTerm( ratioTerm );
 
     const changeAmount = globalKeyStateTracker.shiftKeyDown ? this.shiftKeyboardStep : this.keyboardStep;
     const valueDelta = changeAmount * ( increment ? 1 : -1 );
@@ -133,11 +133,11 @@ class BothHandsInteractionListener {
     // Because this interaction uses the keyboard, snap to the keyboard step to handle the case where the hands were
     // previously moved via mouse/touch. See https://github.com/phetsims/ratio-and-proportion/issues/156
     const newValue = inputMapper( currentValueFromTuple + valueDelta, currentValueFromTuple, globalKeyStateTracker.shiftKeyDown, this.inProportionProperty.value );
-    const newRatioTuple = tupleField === 'antecedent' ? this.ratioTupleProperty.value.withAntecedent( newValue ) : this.ratioTupleProperty.value.withConsequent( newValue );
+    const newRatioTuple = this.ratioTupleProperty.value.withValueForTerm( newValue, ratioTerm );
 
     this.ratioTupleProperty.value = newRatioTuple.constrainFields( this.enabledRatioTermsRangeProperty.value );
 
-    this.tickMarkBumpSoundClip.onInteract( this.ratioTupleProperty.value[ tupleField ] );
+    this.tickMarkBumpSoundClip.onInteract( this.ratioTupleProperty.value.getForTerm( ratioTerm ) );
 
     this.onInput();
   }
@@ -160,19 +160,19 @@ class BothHandsInteractionListener {
 
       if ( key === KeyboardUtils.KEY_DOWN_ARROW ) {
         this.consequentInteractedWithProperty.value = true;
-        this.onValueIncrementDecrement( 'consequent', this.consequentMapKeyboardInput, false );
+        this.onValueIncrementDecrement( RatioTerm.CONSEQUENT, this.consequentMapKeyboardInput, false );
       }
       else if ( key === KeyboardUtils.KEY_UP_ARROW ) {
-        this.onValueIncrementDecrement( 'consequent', this.consequentMapKeyboardInput, true );
+        this.onValueIncrementDecrement( RatioTerm.CONSEQUENT, this.consequentMapKeyboardInput, true );
         this.consequentInteractedWithProperty.value = true;
       }
       else if ( key === KeyboardUtils.KEY_W ) {
         this.antecedentInteractedWithProperty.value = true;
-        this.onValueIncrementDecrement( 'antecedent', this.antecedentMapKeyboardInput, true );
+        this.onValueIncrementDecrement( RatioTerm.ANTECEDENT, this.antecedentMapKeyboardInput, true );
       }
       else if ( key === KeyboardUtils.KEY_S ) {
         this.antecedentInteractedWithProperty.value = true;
-        this.onValueIncrementDecrement( 'antecedent', this.antecedentMapKeyboardInput, false );
+        this.onValueIncrementDecrement( RatioTerm.ANTECEDENT, this.antecedentMapKeyboardInput, false );
       }
       else {