Take it to any Survey Company who perform calibration, usually cost =C2=A320.oo.
Google 2 pin test this will indicate how to check and calibrate a dumpy level, the s10 u=
ses the same principles except you have to remove 1/2 error on bubble until it remains=
central throughout 360 degree rotation =

This instrument has an accuracy of plus or minus 6 mm in contrast to a modern dumpy leve=
l accuracy of 2.5 mm.
The disadvantage with the Watts level is that on each individual sighting you have to=
manually set the leveling bubble. With today's modern Dumpy as long as the instrumen=
t remains inside the Bullseye the self leveling compensator will eradicate any leve=
ling error and accuracy will be maintained.

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