# Variance plane - gen 3 - DECam

**URL:** <https://www.rubin.community/t/variance-plane-gen-3-decam/7240>\
**Category:** Support\
**Created:** [November 24, 2022, 2:31am UTC](https://www.rubin.community/t/variance-plane-gen-3-decam/7240 "2022-11-24T02:31:58Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Paula](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/paula/32/1441_2.png) [@Paula](https://www.rubin.community/u/Paula)\
**Post date:** [November 24, 2022, 2:31am UTC](https://www.rubin.community/t/variance-plane-gen-3-decam/7240/1 "2022-11-24T02:31:58Z")

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Hi all 🙂  
I was wondering what is the algorithm/formula that creates the variance plane attached to the calibrated exposure? (`calexp.variance.array`) I haven’t been able to find the script/documentation where this step takes place.

Thanks.

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**Author:** ![timj](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/timj/32/10_2.png) [@timj](https://www.rubin.community/u/timj)\
**Post date:** [November 28, 2022, 5:49pm UTC](https://www.rubin.community/t/variance-plane-gen-3-decam/7240/2 "2022-11-28T17:49:39Z")

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> [@Paula](#):
>
> I haven’t been able to find the script/documentation

A quick search suggests that it is calculated in `isrTask`:

> <https://github.com/lsst/ip_isr/blob/main/python/lsst/ip/isr/isrTask.py#L516-L521>

@czw can point you at specific algorithms.