Electronic stylus force gauge question

Q: Can someone explain the problem with my stylus gauge; it's acting wonky when I take a reading for my cart at 1.75g?

A: Why on earth are you so obsessed with tracking at 1.75g?

I'm no logician, but I believe informally we can call that a non sequitur. I agree though that some non sequiturs can prove educational.

I had a similar experience recently with my cheap electronic gauge and a new cart. The reading would go negative as the stylus approached (but did not touch), and if I hover the stylus a bit above the gauge, the reading would go all over the place. This had never happened before with my other carts, so I naturally blamed first the fan that was on, then the air conditioning, and finally the batteries. None of the above. It was the new cart's interaction with the gauge. I know this because I just swapped back to an old cart and the reading is stable and repeatable (as usual)--with the air and fan on.

I have no idea what about the cart's interaction with the gauge is causing the disturbance, but I share Actusreus's concern about getting a repeatable number in such circumstances (my fluctuations were far more wild than his, but even so). The reasons are for this concern are none of your business ;-)

I always have similar but not exactly identical problem with most of my cartridges. If I turn on digital scale on first and let it zero first, as soon as I move my cartridge over the scale, it gave negative reading. However the number usually does not fluctuate wildly. The reading is very much reproducible every time. I assume it was just magnetic interference from cartridge or something along that line. Usually I just move my cartridge above the scale first then turn the scale on and let it zero itself then. This happened with my airtight koetsu dynavetor and Lyra with 2 different scale (same made though) so I thought it was normal.

Just to add to the fun, I have three arms mounted on two tables, and in each case, my cheap digital scale tells me that the VTF varies depending on where I put the scale on the respective turntables. That is, it measures slightly differently depending on whether the scale is placed where the lead-in grooves are, or half-way in, or where the end grooves are. I find this curious but not really important. Certainly trying to pinpoint 1.75 g -- as opposed to l.72 or 1.78 or whatever -- is not in the cards for me :-)

Here is another thought as a way to check the condition of your tonearm bearings in the vertical direction. After placing the stylus on your VTF gage and getting a reading, apply a light pressure downward on your counterweight to bring the VTF to near zero and then let go. If the scale has a new reading, that difference is called hysteresis. e.g. let's say your scale reads 1.5g and then you apply a pressure to your counterweight until the scale reads near zero, let go and now the scale reads 1.49g. The hysteresis is the percent difference or in this case 0.67%. For mechanical systems, up to 1% hysteresis is very good. Up to 2% is ok, but considering the quality of our tonearms and bearings used, I would expect it to be less than 1%. Try it in the other direction too. Apply a slight upward pressure on the counterweight to raise VTF by 0.5g or so and then release.
So why is hysteresis a factor? Because as the tonearm/cartridge tracks over a record, any waviness in the record causes the tonearm to move up and down. If the bearings have too much hysteresis then the VTF will be changing slightly- going higher as the tonearm is pushed upward and then being a little lighter as the tonearm comes back down. Aside from inertia, 0% hysteresis means the VTF would stay constant as the stylus tracks over a wavy record.
The scale itself should have extremely low hysteresis since it is a strain gage. Good quality scales that I have used change maybe one digit out to the third decimal place when I have added/subtracted the load slightly.

Suteetat
I always have similar but not exactly identical problem with most of my cartridges. If I turn on digital scale on first and let it zero first, as soon as I move my cartridge over the scale, it gave negative reading. However the number usually does not fluctuate wildly. The reading is very much reproducible every time. I assume it was just magnetic interference from cartridge or something along that line. Usually I just move my cartridge above the scale first then turn the scale on and let it zero itself then. This happened with my airtight koetsu dynavetor and Lyra with 2 different scale (same made though) so I thought it was normal.

Suteetat (and others),
Do you have any concerns that the magnetic interference might negatively affect the cartridge long term? Beyond inconsistent readings, the icing on the cake would be to damage a few $K cartridge with a cheap scale while trying to dial in the VTF!