--- title: constantSideOnHeightCalculation property for bottom rails description: How to configure whether the internal or external bottom rail height kept constant when making changes. --- [Skip to content](https://knowledgehub.endtoendit.com/knowledgebase/constantsideonheightcalculation-property-for-bottom-rails#main-content) [![integrate knowledge base](https://knowledgehub.endtoendit.com/hs-fs/hubfs/integrate%20knowledge%20base.jpg?width=386&height=34&name=integrate%20knowledge%20base.jpg)](https://knowledgehub.endtoendit.com/knowledgebase?hsLang=en) Open main navigation Close main navigation - [endtoendit.com](https://endtoendit.com/) [endtoendit.com](https://endtoendit.com/) Hello. How can we help you? - There are no suggestions because the search field is empty. 1. [integrate Support Team Knowledge Base](https://knowledgehub.endtoendit.com/knowledgebase?hsLang=en) 2. [integrateDrawingBoard](https://knowledgehub.endtoendit.com/knowledgebase/integratedrawingboard?hsLang=en) 3. [Operational & System Settings](https://knowledgehub.endtoendit.com/knowledgebase/integratedrawingboard?hsLang=en#operational-system-settings) # constantSideOnHeightCalculation property for bottom rails ## This property allows you to set whether the internal or external measurement is prioritised when making changes that affect bottom rails. **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. ![image2 (1)](https://knowledgehub.endtoendit.com/hs-fs/hubfs/image2%20(1).png?width=283&height=561&name=image2%20(1).png)  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.  ![image3](https://knowledgehub.endtoendit.com/hs-fs/hubfs/image3.png?width=312&height=596&name=image3.png)  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 willstay constant, and measurements marked with red (internal sash heights) will be recalculated.   ![image4](https://knowledgehub.endtoendit.com/hs-fs/hubfs/image4.png?width=301&height=547&name=image4.png)  **For complete new windows, since overall frame height is calculated based on internal sash height, frame height will change in this scenario.**   - [integrateCRM Module](https://knowledgehub.endtoendit.com/knowledgebase/integratecrm-module?hsLang=en#main-content) - [Leads & Prospects](https://knowledgehub.endtoendit.com/knowledgebase/integratecrm-module?hsLang=en#leads-prospects) - [Emails & Templates](https://knowledgehub.endtoendit.com/knowledgebase/integratecrm-module?hsLang=en#emails-templates) - [Tasks, Appointments & Reminders](https://knowledgehub.endtoendit.com/knowledgebase/integratecrm-module?hsLang=en#tasks-appointments-reminders) - [Quotes & Orders](https://knowledgehub.endtoendit.com/knowledgebase/integratecrm-module?hsLang=en#quotes-orders) - 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