# Need Help On Expression Binding

**URL:** <https://forum.inductiveautomation.com/t/need-help-on-expression-binding/21487>\
**Category:** Ignition\
**Created:** [December 19, 2018, 6:23am UTC](https://forum.inductiveautomation.com/t/need-help-on-expression-binding/21487 "2018-12-19T06:23:23Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![subramaniam.gopal](https://avatars.discourse-cdn.com/v4/letter/s/49beb7/32.png) [@subramaniam.gopal](https://forum.inductiveautomation.com/u/subramaniam.gopal)\
**Post date:** [December 19, 2018, 6:23am UTC](https://forum.inductiveautomation.com/t/need-help-on-expression-binding/21487/1 "2018-12-19T06:23:23Z")

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({Root Container.PIDProcessVal::ProcessHiVal})-({Root Container.PIDProcessVal::ProcessLoVal})/5

error msg appear “caused by ExpressionException: Expression left operand is null.”

need to perform calculation using parameter value please suggest how to perform.

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**Author:** ![c.bertulli](https://avatars.discourse-cdn.com/v4/letter/c/f19dbf/32.png) [@c.bertulli](https://forum.inductiveautomation.com/u/c.bertulli)\
**Post date:** [December 19, 2018, 9:13am UTC](https://forum.inductiveautomation.com/t/need-help-on-expression-binding/21487/2 "2018-12-19T09:13:36Z")

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Are you sure about the double : ? ({Root Container.PIDProcessVal **::** ProcessHiVal})  
I suppose “ProcessHiVal” and “ProcessLoVal” are custom properties, right?  
In this case the line should be `{Root Container.PIDProcessVal.ProcessHiVal}-{Root Container.PIDProcessVal.ProcessLoVal}/5`.  
Also, you know that your expression ( as you wrote it ) will do ProcessHiVal - the result of ProcessLoVal / 5, right?

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<div class="post-metadata">

**Author:** ![subramaniam.gopal](https://avatars.discourse-cdn.com/v4/letter/s/49beb7/32.png) [@subramaniam.gopal](https://forum.inductiveautomation.com/u/subramaniam.gopal)\
**Post date:** [December 19, 2018, 9:59am UTC](https://forum.inductiveautomation.com/t/need-help-on-expression-binding/21487/3 "2018-12-19T09:59:09Z")

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hi bertulli thanks for your reply, tried with syntax you have provided butfollowing error msg is coming  
Unable to find component for path: ‘Root Container.PIDProcessVal.ProcessHiVal’

im using custom properties mapped with UDT i need to use that tag for calculation kindly suggest better way if you have any. i am using this calculation for Major Tick Span calculation. (im calculating difference between max and min value and divide by 5 )

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**Author:** ![c.bertulli](https://avatars.discourse-cdn.com/v4/letter/c/f19dbf/32.png) [@c.bertulli](https://forum.inductiveautomation.com/u/c.bertulli)\
**Post date:** [December 19, 2018, 10:24am UTC](https://forum.inductiveautomation.com/t/need-help-on-expression-binding/21487/4 "2018-12-19T10:24:00Z")

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Are you using a “Numeric Text Field” named “PIDProcessVal” with two custom properties named “ProcessHiVal” and “ProcessLoVal”?  
What component are you using for “calculation for Major Tick Span calculation”?

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<div class="post-metadata">

**Author:** ![subramaniam.gopal](https://avatars.discourse-cdn.com/v4/letter/s/49beb7/32.png) [@subramaniam.gopal](https://forum.inductiveautomation.com/u/subramaniam.gopal)\
**Post date:** [December 19, 2018, 10:29am UTC](https://forum.inductiveautomation.com/t/need-help-on-expression-binding/21487/5 "2018-12-19T10:29:42Z")

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PIDProcessVal is UDT (Datatype) defined tag.  
ProcessHiVal and ProcessLoVAL are tags in that UDT  
im passing the value to a POPUP where im using the Linear Scale i need to dynamically calculate the Major Tick Span for that POPUP.

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**Author:** ![c.bertulli](https://avatars.discourse-cdn.com/v4/letter/c/f19dbf/32.png) [@c.bertulli](https://forum.inductiveautomation.com/u/c.bertulli)\
**Post date:** [December 19, 2018, 11:02am UTC](https://forum.inductiveautomation.com/t/need-help-on-expression-binding/21487/6 "2018-12-19T11:02:27Z")

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Ok, now I understand what you are trying to achieve.  
Check this documentation, it should help you out 😉 [https://docs.inductiveautomation.com/display/DOC79/Parameterized+Popup+Window+and+UDTs](https://docs.inductiveautomation.com/display/DOC79/Parameterized+Popup+Window+and+UDTs)

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<div class="post-metadata">

**Author:** ![subramaniam.gopal](https://avatars.discourse-cdn.com/v4/letter/s/49beb7/32.png) [@subramaniam.gopal](https://forum.inductiveautomation.com/u/subramaniam.gopal)\
**Post date:** [December 19, 2018, 4:09pm UTC](https://forum.inductiveautomation.com/t/need-help-on-expression-binding/21487/7 "2018-12-19T16:09:09Z")

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thanks Bertulli. pls share link if have any user manual for component binding in details

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<div class="post-metadata">

**Author:** ![c.bertulli](https://avatars.discourse-cdn.com/v4/letter/c/f19dbf/32.png) [@c.bertulli](https://forum.inductiveautomation.com/u/c.bertulli)\
**Post date:** [December 19, 2018, 4:31pm UTC](https://forum.inductiveautomation.com/t/need-help-on-expression-binding/21487/8 "2018-12-19T16:31:03Z")

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Well this -\> [https://docs.inductiveautomation.com/](https://docs.inductiveautomation.com/) is the Ignition’s Manual link.  
If you want something in details, in this case “binding”, you can search it inside the “Search” text field.