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        <esri:PrintParameters id="printParameters"                               format="{formatsDDL.selectedItem}"                               layoutTemplate="{layoutTemplatesDDL.selectedItem}"                               map="{hostBaseWidget.map}"                               preserveScale="{scaleCheckbox.selected}">             <esri:layoutOptions>                 <esri:LayoutOptions id="layoutOptions">                     <esri:scaleBarOptions>                         <esri:ScaleBarOptions nonMetricUnit="esriFeet"/>                     </esri:scaleBarOptions>                 </esri:LayoutOptions>             </esri:layoutOptions>         </esri:PrintParameters>You'll need to set PrintParameters.layoutOptions.scaleBarOptions.nonMetricUnit.
See:
http://resources.arcgis.com/en/help/flex-api/apiref/com/esri/ags/tasks/supportClasses/ScaleBarOption...
        <esri:PrintParameters id="printParameters"                               format="{formatsDDL.selectedItem}"                               layoutTemplate="{layoutTemplatesDDL.selectedItem}"                               map="{hostBaseWidget.map}"                               preserveScale="{scaleCheckbox.selected}">             <esri:layoutOptions>                 <esri:LayoutOptions id="layoutOptions">                     <esri:scaleBarOptions>                         <esri:ScaleBarOptions nonMetricUnit="esriFeet"/>                     </esri:scaleBarOptions>                 </esri:LayoutOptions>             </esri:layoutOptions>         </esri:PrintParameters>You would need to recompile the PrintWidget with this change to the PrintParameters inside ExportWebMapForm.mxml:<esri:PrintParameters id="printParameters" format="{formatsDDL.selectedItem}" layoutTemplate="{layoutTemplatesDDL.selectedItem}" map="{hostBaseWidget.map}" preserveScale="{scaleCheckbox.selected}"> <esri:layoutOptions> <esri:LayoutOptions id="layoutOptions"> <esri:scaleBarOptions> <esri:ScaleBarOptions nonMetricUnit="esriFeet"/> </esri:scaleBarOptions> </esri:LayoutOptions> </esri:layoutOptions> </esri:PrintParameters>