constantSideOnHeightCalculation is a property available in the Default Values page (/PricingAndConfig/DrawingBoardConfig/DefaultValue) for all parts that have a bottom rail.
The property determines whether the internal or external measurement is kept constant when changes are made. These include changes to the bottom rail shape, the chamfer angle or step size, and the sash thickness.
When setting default values, it is important to make sure that this property matches the default value that is set for the bottom rail height: if bottomHeight is defined, constantSideOnHeightCalculation should be set to internal; if bottomHeightExternal is defined, constantSideOnHeightCalculation should be set to external.
Example
Take a pair of sliding sashes with a chamfered bottom rail.
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When reducing the current 60mm sash thickness to 40mm, we are essentially trimming off 20mm from one side of the item.
If constantSideOnHeightCalculation is set to internal_height, we are effectively losing 20mm from the external face of the item.
As a result all measurements marked with green will stay constant, and measurements marked with red (external sash heights) will be recalculated.
If constantSideOnHeightCalculation is set to external_height we are effectively losing 20mm from the internal face of the item.
As a result all measurements marked with green will stay constant, and measurements marked with red (internal sash heights) will be recalculated.
For complete new windows, since overall frame height is calculated based on internal sash height, frame height will change in this scenario.