Fixed calculation of per-stage resource mass
Fixed calculation of per-stage resource mass

--- a/KerbalEngineer/VesselSimulator/Simulation.cs
+++ b/KerbalEngineer/VesselSimulator/Simulation.cs
@@ -531,7 +531,7 @@
 
                 // Store the magnitude of the deltaV vector
                 stage.deltaV = this.vecStageDeltaV.magnitude;
-                stage.resourceMass = this.stepStartMass - this.stepEndMass;
+                stage.resourceMass = this.stageStartMass - this.stepEndMass;
 
                 // Recalculate effective stage isp from the stage deltaV (flip the standard deltaV calculation around)
                 // Note: If the mass doesn't change then this is a divide by zero