Cartridge for Graham 1.5

Carl, does the scale look like this one - new VTF scale
If so, that scale reads about 0.2g higher than my scale that measures exactly at record level. The scale is shown measuring a 1 yen coin (nominally 1g).
With 1g test weights placed directly on the measuring platforms, both of my scales read the same.

Here are a couple of old pics I took of the pocket scale/wally adapter.
Pocket scale weighing 1 yen coin
Wallyscale clone

Tobes,

Yes, we theoretically should adjust VTF for different record thicknesses. And, we have a more difficult issue with warped records.

Please forgive me if this is ground you have already covered, but there is a real reason for what you have observed. For the Graham 1.5 and for many unipivot arms, the center of gravity is designed to be below the pivot point. This results in a small but real force that acts to restore the arm to the correct positioning with the stylus at the record surface -- any deflection of the arm (such as the stylus lifting above the record surface) causes the VTF to vary. It is analogous to a pendulum wanting to be perfectly vertical, experiencing a force pushing it toward the perfectly vertical position when it is deflected. At one stage of the evolution of unipivot arms, this may have been considered a desirable characteristic because it contributed to the arm's dynamic stability.

Bob Graham has eliminated this effect in his new Phantom arm by designing the center of gravity to be at the pivot point. He instead achieves arm stability with the help of a magnet.

When I set up my 1.5, now upgraded to a 2.2, I needed to be careful how high my weigh scale was when setting my VTF. It needed to be as close as possible to the height of the actual record surface, or else I would have suffered a different VTF than what I wanted. You and Carl have both observed this effect. It sounds to me like your scales are close to accurate, but their heights were different.

Thanks for the photos Tobes. I have the first one accurate to 0.002 +-?. I looked at my Orbe and made a block about 1/8 lower than the platter height. My gauge on platter says 2.152. Gauge on my block says 2.105. It seems as though Jameswei is correct in that the Graham is pushing down somewhat. In my poor mind I don't see it but then again its late and the difference here is below my tolerance level. Learned something new again!
Carl

I think, you've done your decision, but when you are looking for something special, do a search for a Incognito 'Shibui'.
A very remarkable cartridge for the money.

Yes the scale has .002g precision. Unfortunately this precision is offset by inaccuracy caused by not measuring at record height. Nonetheless, it can still be used as a reference point.
Best to make fine adjustment of VTF by ear anyway (though I like to take a measurement so I can repeat the setup if swapping cartridges etc).
As you said, listening is more fun than obsessing over the actual VTF - as long as it is set for best sound.

The whole thing with the arm height helps explain the anomalies that have been bugging me with VTF measurements on the Graham. I agree it does seem counter-intuitive though.
Thanks for your input James.
Cheers, Paul