bug fix for html slider range that didn't align with step value, #535

js/common/model/RAPRatio.ts

@@ -35,6 +35,10 @@ const DEFAULT_TERM_VALUE_RANGE = rapConstants.TOTAL_RATIO_TERM_VALUE_RANGE;
 // because that threshold value, by definition, will unlock the ratio, see https://github.com/phetsims/ratio-and-proportion/issues/257#issuecomment-748285667
 const LOCK_RATIO_RANGE_MIN = rapConstants.NO_SUCCESS_VALUE_THRESHOLD + Number.EPSILON;
 
+// This value needs to be an "even and round" number as it pertains to the step size of the sliders that control the ratio.
+// See https://github.com/phetsims/ratio-and-proportion/issues/535
+assert && assert( LOCK_RATIO_RANGE_MIN === 0.01, 'please be careful when changing this' );
+
 class RAPRatio {
 
   // Keep two references so that this can be public readonly, AND changed internally.

js/common/rapConstants.ts

@@ -57,7 +57,7 @@ class RAPConstants extends PhetioObject {
 
   // The value in which when either the antecedent or consequent is less than this, the ratio cannot be "in proportion".
   // Add .001 to support two keyboard nav motions above 0 (counting the min range being >0).
-  public NO_SUCCESS_VALUE_THRESHOLD = 0.01;
+  public NO_SUCCESS_VALUE_THRESHOLD = 0.01 - Number.EPSILON;
 
   public QUERY_PARAMETERS = RAPQueryParameters;