# Difference between Min Max of Historical tag over set time

**URL:** <https://forum.inductiveautomation.com/t/difference-between-min-max-of-historical-tag-over-set-time/54174>\
**Category:** Ignition\
**Tags:** ignition81, database, vision, scripting\
**Created:** [December 15, 2021, 10:55pm UTC](https://forum.inductiveautomation.com/t/difference-between-min-max-of-historical-tag-over-set-time/54174 "2021-12-15T22:55:43Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![xtristan](https://avatars.discourse-cdn.com/v4/letter/x/ba8739/32.png) [@xtristan](https://forum.inductiveautomation.com/u/xtristan)\
**Post date:** [December 15, 2021, 10:55pm UTC](https://forum.inductiveautomation.com/t/difference-between-min-max-of-historical-tag-over-set-time/54174/1 "2021-12-15T22:55:43Z")

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I’m looking for a way to find the difference between a tag at a specific start time vs system.date.now(). Ideally the Calculated Pen function would be able to check the difference between two Calculated Pens instead of only being able to work on Tag History Pens but that doesn’t seem to be the case.

Any help is appreciated