API Reference > imodeljs-frontend > QuantityFormatting > QuantityFormatter > onActiveUnitSystemChanged onActiveUnitSystemChanged Readonly Deprecated use onActiveFormattingUnitSystemChanged event for multiple unit system support. onActiveUnitSystemChanged: BeUiEvent<{ useImperial: boolean }> = ... Called after the active unit system is changed. The useImperial argument should not be relied on now that multiple systems are supported. It will only return true if unit system is explicitly set to "imperial" Defined in core/frontend/src/quantity-formatting/QuantityFormatter.ts Line 326 Last Updated: 12 June, 2024