# Expression to lookup the value of an historical tag

**URL:** <https://forum.inductiveautomation.com/t/expression-to-lookup-the-value-of-an-historical-tag/44286>\
**Category:** Ignition\
**Created:** [March 10, 2021, 4:33am UTC](https://forum.inductiveautomation.com/t/expression-to-lookup-the-value-of-an-historical-tag/44286 "2021-03-10T04:33:06Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![mcurtis](https://avatars.discourse-cdn.com/v4/letter/m/3da27b/32.png) [@mcurtis](https://forum.inductiveautomation.com/u/mcurtis)\
**Post date:** [March 10, 2021, 4:33am UTC](https://forum.inductiveautomation.com/t/expression-to-lookup-the-value-of-an-historical-tag/44286/1 "2021-03-10T04:33:06Z")

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I need some help please to correctly write an expression tag that will lookup the value of an historical tag and then subtract it from the current tag value and write the result to a new tag. Something along the lines of;

MyTag2 = {MyTag1@date.now() - MyTag1@date.now(), -15, “minute”}

Many thanks.