# Unit Conversion on Historical Data

**URL:** <https://forum.inductiveautomation.com/t/unit-conversion-on-historical-data/10826>\
**Category:** Ignition\
**Created:** [November 25, 2015, 7:25pm UTC](https://forum.inductiveautomation.com/t/unit-conversion-on-historical-data/10826 "2015-11-25T19:25:22Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![denji26](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/denji26/32/5805_2.png) [@denji26](https://forum.inductiveautomation.com/u/denji26)\
**Post date:** [November 25, 2015, 7:25pm UTC](https://forum.inductiveautomation.com/t/unit-conversion-on-historical-data/10826/1 "2015-11-25T19:25:22Z")

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I have a requirement to be able to change units when displaying data. I’ve got real time data locked down, and I can use calculated tags to display most historical data, but I’m not sure how I am going to handle displaying historical temperature data.

Any suggestions?

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**Author:** ![denji26](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/denji26/32/5805_2.png) [@denji26](https://forum.inductiveautomation.com/u/denji26)\
**Post date:** [November 25, 2015, 8:43pm UTC](https://forum.inductiveautomation.com/t/unit-conversion-on-historical-data/10826/2 "2015-11-25T20:43:22Z")

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After playing around a bit and looking at other posts I believe I have a method that will work for me.

Instead of converting the value, I am going to use the linear scale component to create my Y-Axis scaled how I need, then overwrite the X-Trace label to display the converted value.

For display purposes, the value should appear converted.

Still would be interested in hearing if there is a way to convert temperature for historical trends, maybe create custom calculated tag functions?

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**Author:** ![diat150](https://avatars.discourse-cdn.com/v4/letter/d/a587f6/32.png) [@diat150](https://forum.inductiveautomation.com/u/diat150)\
**Post date:** [November 25, 2015, 9:34pm UTC](https://forum.inductiveautomation.com/t/unit-conversion-on-historical-data/10826/3 "2015-11-25T21:34:31Z")

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another option would be to use the queryTagHistory function to pull back a dataset, then use python to iterate thru that dataset and convert your values. Then push that to a classic chart. just a thought.