# Meaning of \`g\_psfFluxSigma\`

**URL:** <https://www.rubin.community/t/meaning-of-g-psffluxsigma/11900>\
**Category:** Lasair\
**Created:** [April 23, 2026, 9:45am UTC](https://www.rubin.community/t/meaning-of-g-psffluxsigma/11900 "2026-04-23T09:45:12Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![ChrisFro](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/chrisfro/32/4082_2.png) [@ChrisFro](https://www.rubin.community/u/ChrisFro)\
**Post date:** [April 23, 2026, 9:45am UTC](https://www.rubin.community/t/meaning-of-g-psffluxsigma/11900/1 "2026-04-23T09:45:13Z")

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Hi,

Is the column `objects_ext.g_psfFluxSigma` the uncertainty on the `objects.g_psfFlux`, i.e. the uncertainty on the latest observation in that filter?

Both Lasair schema and LSST Schema browser say: ‘Standard deviation of the distribution of g\_psfFlux’  
This is worded slightly ambiguously because it could either be the std of _all_`g_psfFlux` measurements or just the latest.

Thanks!  
Chris

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**Author:** ![roy](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/roy/32/1254_2.png) [@roy](https://www.rubin.community/u/roy)\
**Post date:** [April 23, 2026, 10:06am UTC](https://www.rubin.community/t/meaning-of-g-psffluxsigma/11900/2 "2026-04-23T10:06:07Z")

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Its copied [directly from Rubin](https://github.com/lsst/alert_packet/blob/main/python/lsst/alert/packet/schema/10/0/lsst.v10_0.diaObject.avsc#L125-L133). I suggest raise this on another sub-forum so Eric will answer it.

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**Author:** ![galaxyumi331](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/galaxyumi331/32/2677_2.png) [@galaxyumi331](https://www.rubin.community/u/galaxyumi331)\
**Post date:** [April 23, 2026, 5:52pm UTC](https://www.rubin.community/t/meaning-of-g-psffluxsigma/11900/3 "2026-04-23T17:52:36Z")

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Hi @ChrisFro ,

I am referring to Section 2.2.4 of [NB tutorial 201.4](https://dp1.lsst.io/tutorials/notebook/201/notebook-201-4.html) regarding difference-image photometry and the [DP1 `DiaObject` table schema](https://sdm-schemas.lsst.io/dp1.html#DiaObject). In this context, `g_psfFluxSigma` represents the standard deviation of the distribution of `g_psfFlux` for a given object. In contrast, `g_psfFluxErrMean` is the standard error on the weighted mean of diaSource PSF fluxes. In case this isn’t the answer you were looking for, feel free to unmark the solution and we can keep looking into it.