Measuring VTF with electronic gauge....

What matters is that VTF be measured with the stylus at the same level as when playing a record. Some arms because of their design can cause VTF to change as the angle of the arm changes. So in other words you want a gauge that works like chakster said, with the stylus at LP level. Not LP level plus the gauge. LP level.   

VTF btw is always specified as a range. Anything within that range is perfectly acceptable. Within that range however VTF is set by ear. If you like it at the high end of the range then that is the "correct" VTF for you. Precision therefore is only a factor to the extent it keeps your "by ear" setting from being too high or low.

My cheap Chinese scale is the exactly the same level as an average LP.   
Nyah nyah.
Of course vinyl comes in different thicknesses.
What to do? You can adjust to each platter...
OR. 
Enjoy the music.

millercarbon
Has nailed it but that is only the start of the fine tune process..

Depending on stylus shape (and not using simple conical shape that they do not care about VTA).
You may consider that if you like for example by ear to be in the upper/lower range of the VTF. Then that means you have also in the same time when you adjust VTF inderectly also adjusted the VTA.

So it could in other words be that you by ear actually liked the sound of the different VTA..

So when adjusting a TT it is NOT just to adjust VTF then done.. When altering VTF you are also inderectly altering VTA and antiscating (in some extent also overhang but that is nitpicking.. but i have been there.)

So if we really want to adjust a TT for the best sound for you then you do it by ear and the procedure goes in circles.

In the way that when you have a more advanced stylus shape than conical. And you are you are preferred the sound near max VTF than that can be a sign that you also may be liking a lower VTA.. 

So how can you know if it the positive sound quality increase came from added VTF or lowered VTA?

The first cycle is done. Proceed with second cycle of adjustment by lowering (or vice versa) the tonearm/VTA and adjust by ear again VTF. (Now you got the ability to hear the difference between the two parameters).

So you go in "circles" and iterate trough each adjustment one by one. And each iteration the adjustment window and fine tuning will be smaller and smaller. Until you find nirvana and can start to enjoy the stylus for several hundreds of hours!

So in summary the more expensive stylus shape we get the ability to do more adjustment and fine-tuning and it also eneble us to do that.

That we are not wasting your time and money by sitting in a F1 car during rush hour traffic when you were better of being in a Toyota Prius with AC. 

(A pro tip is to adjust VTF to the lowest range and listening (same record and track and something with a repeatable bass line) then do the same thing again but with max range VTF. To hear and learn what the difference is and you know/learn what to listening for/after.
And if you do not hear any difference at all then there is several reasons why that would be. But until those "issue/s" is not corrected then it is a waste to spending the time to make the adjustments above or to buy a F1 car when a Prius is more suitable in that situation.)

I use a cheap "battered" old LP bought for virtually nothing from a charity shop. Cleaned it up of course and never played, but used solely as a set up LP for when my cartridge has been retipped. Then I use my ears !!!

Recommended vtf at lp level and then fine tune with ear.