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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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  
I watched someone doing a setup where three different digital scales were used and none of the scales agreed (the user averages the readings).  None of the scales were low-cost models, one was a Win scale that is made for cartridge setup and costed about $900 more than 15 years ago.

I don't know what to make of this.  I use an outrigger that rests on the scale which has an attachment that can be set at different heights so that the measurement is taken at the level of the record.  This also means that the cartridge is never close to the scale itself (the outrigger is acrylic).  I don't know if this improves accuracy, but, it certainly removes issues involving magnetic attraction of the cartridge to components in the scale, and incorrect readings from the cartridge being at the wrong position (height) when the measurement is taken.
Exactly Larryi.

I never even thought about the magnetic part of measuring on the outrigger bracket, just the fact that it now sits at correct height but it certainly could be a part of it.
To the OP:  Lower the cartridge (preferably an MC cartridge, because they have big magnets) until it is barely above the weigh pan but not touching it. Does the gauge show a negative weight value?  If so, that indicates it contains some low level of iron; the magnet in the cartridge is pulling UP on the pan.  If the weigh pan is magnetic, even a little bit, that messes things up.  I used one of the popular digital scales for years before realizing that it had the problem, which was only evident when I tried to adjust VTF for an Ortofon MC2000 cartridge, which has a humongous magnet situated in its belly, near to the platter or any weigh pan.  I subsequently bought one of the 2 or 3 gauges made by Ortofon, the weigh pan of which so far seems to be non-ferrous, although it is metal.  This problem seems so easy to avoid in designing such a gauge.  But apparently the sellers do not care a fig.  As long as they're selling.
I still use the old Technics that came with the EPA-100 arm. It's electronic but analog, not digital, and doesn't give you milligrams (which are SO important). It's just a needle that swings from .5g to 3g, with markings for each .1g — and I can squeeze the needle between them for .05g. Accurate enough for me, and utterly consistent. Not high tech, but cool in a retro way.