# Graph of windage - minus wind?

**URL:** <https://community.tempest.earth/t/graph-of-windage-minus-wind/4896>\
**Category:** Tempest Owners\
**Created:** [December 9, 2019, 4:52pm UTC](https://community.tempest.earth/t/graph-of-windage-minus-wind/4896 "2019-12-09T16:52:52Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![acyducy](https://sea2.discourse-cdn.com/flex020/user_avatar/community.tempest.earth/acyducy/32/5985_2.png) [@acyducy](https://community.tempest.earth/u/acyducy)\
**Post date:** [December 9, 2019, 4:52pm UTC](https://community.tempest.earth/t/graph-of-windage-minus-wind/4896/1 "2019-12-09T16:52:52Z")

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New to this and learning how it works.  
My graph of wind is showing (But not always)

 ![image](https://us1.discourse-cdn.com/flex020/uploads/sws/original/2X/e/ef62e44834263b33953a80a34b4d3e1a2508feb8.jpeg) a negative wind speed at the beginning and end of a wind gust period and averages. I don’t see this on others pages.  
Is this a defect? Or calibration issue?  
How can I rectify this apparent error?  
Thank you.  
Don

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**Author:** ![eric](https://sea2.discourse-cdn.com/flex020/user_avatar/community.tempest.earth/eric/32/13553_2.png) [@eric](https://community.tempest.earth/u/eric)\
**Post date:** [December 9, 2019, 5:25pm UTC](https://community.tempest.earth/t/graph-of-windage-minus-wind/4896/2 "2019-12-09T17:25:05Z")

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I think this is related to the graphing library used and not the measurements. It is interpolating between values and goes over the line when null values are used …

Guess only a WF coder can confirm (or not)

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**Author:** ![sunny](https://sea2.discourse-cdn.com/flex020/user_avatar/community.tempest.earth/sunny/32/16368_2.png) [@sunny](https://community.tempest.earth/u/sunny)\
**Post date:** [December 9, 2019, 10:24pm UTC](https://community.tempest.earth/t/graph-of-windage-minus-wind/4896/3 "2019-12-09T22:24:45Z")

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the only data used in this graph is where the dots are. The smooth line is because the choice of interpolation method (there are other methods, with different characteristics.). Note this is not only for negative values. You see the same effect at 05:20, the red line dips below the measured value, just to keep it smooth.  
It can even be worse ( [https://community.tempest.earth/t/impossible-graph-rare-interpolation-anomaly](https://community.tempest.earth/t/impossible-graph-rare-interpolation-anomaly) ), which is a pretty unusual artifact, and looks more like a mistake in the implementation. But this situation hardly ever arises with the weatherflow unit.

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**Author:** ![acyducy](https://sea2.discourse-cdn.com/flex020/user_avatar/community.tempest.earth/acyducy/32/5985_2.png) [@acyducy](https://community.tempest.earth/u/acyducy)\
**Post date:** [December 10, 2019, 3:43am UTC](https://community.tempest.earth/t/graph-of-windage-minus-wind/4896/4 "2019-12-10T03:43:16Z")

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Interest graph you had. But negative is still negative. 😬

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**Author:** ![WFstaff](https://sea2.discourse-cdn.com/flex020/user_avatar/community.tempest.earth/wfstaff/32/6006_2.png) [@WFstaff](https://community.tempest.earth/u/WFstaff)\
**Post date:** [December 10, 2019, 3:38pm UTC](https://community.tempest.earth/t/graph-of-windage-minus-wind/4896/5 "2019-12-10T15:38:05Z")

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Indeed this is an artifact; a visual bug. There are no negative values in the record.