Audio Additives Stylus Force Gauge inconstantcy

I recently purchased an Audio Additives Stylus Force Gauge and it is driving me nuts. I get inconstant readings every time I lower the stylus onto the little black dot on the plate. Without moving the arm, every time I lower, raise, lower, etc., I get a different reading between 1.68 - 1.88. The batteries are new, device reads 0.000g at start up, calibration checks out using supplied weight, room temperature is 72F, no interference from tonearm lifter and everything is level.
Anyone else have this problem?
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Put a pair of Depends on it. Should do the trick. Or let it out with the dogs. 
Go onto Amazon and take a look at the Riverstone Audio gauge. $28.95, none better.
Agree 100% with @bdp24 

Bought the Riverstone few years back and never looked back.

Extremely accurate and repeatable, really like the drop down bracket so stylus is then at same height it would be playing vinyl.
My experience with these repackaged generic gauges like the one you are using is that they are all unreliable - perhaps its some form of magnetic interference (i.e. this is why it measures fine on calibration weights but goes haywire with a cart)

The Riverstone that others cite likely does not suffer from this due to the added mechanism offsetting the location point and getting the cartridge magnet away from the weight mechanism. 

These days I use the Rega Gauge which eschews magnetic materials entirely and works a dream but it is rather premium priced