I have a hydraulic one.  They are nice but, the ground mositure had alot to do with it.

If it is dry you may have 500 psi and if it rains and soaks in the next day it may read 250 psi.  you have to take it with a grain of salt i think.

I like a hand fence post auger and pull knife up the hole and see if you are man enough to pull to the top.