# What does eph and epv mean in GPS measurement?

**URL:** <https://discuss.px4.io/t/what-does-eph-and-epv-mean-in-gps-measurement/1645>\
**Category:** Flight Testing & Log Analysis\
**Created:** [November 2, 2016, 3:39am UTC](https://discuss.px4.io/t/what-does-eph-and-epv-mean-in-gps-measurement/1645 "2016-11-02T03:39:48Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![doctorluhang](https://discuss.px4.io/user_avatar/discuss.px4.io/doctorluhang/32/414_2.png) [@doctorluhang](https://discuss.px4.io/u/doctorluhang)\
**Post date:** [November 2, 2016, 3:39am UTC](https://discuss.px4.io/t/what-does-eph-and-epv-mean-in-gps-measurement/1645/1 "2016-11-02T03:39:49Z")

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The position estimation requires increment on each step for eph and epv. What do these params mean in GPS? And, why do they need to be increased upon each measurement?

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**Author:** ![langxm1223](https://discuss.px4.io/user_avatar/discuss.px4.io/langxm1223/32/3948_2.png) [@langxm1223](https://discuss.px4.io/u/langxm1223)\
**Post date:** [November 2, 2016, 9:14am UTC](https://discuss.px4.io/t/what-does-eph-and-epv-mean-in-gps-measurement/1645/2 "2016-11-02T09:14:19Z")

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eph:Standard deviation of horizontal position error, (metres)  
epv:Standard deviation of vertical position error, (metres)  
Maybe the increment occurred in the timeout operation…did not find it in LPE