I believe the Haynes manual for my bike (Street Cup/Twin series) it states 30mm of deflection max. I measure several points using a guide with the min and max marks. I measure loose and tight spots and get an average, shooting for around mid range of 24mm. I use a common spot such as the top of the link, but just as long as you measure consistently it’s fine. With regular maintenance the only time I’ve had to adjust was when I got new tires. 10k miles and the sprockets still look good, but I have the replacements on the shelf.
Which bike and year.....my 2020 T100 the book says....support bike upright.....not on and stand so weight on its wheels. Quite tricky....first time I used ropes in my garage.....one to the top of either rear shock to a fixing on the roof....that worked. Now I sit it on its main stand not side....and add 5mm to the req free play I see.....so if I want 25mm....I set to 30mm....one back on its wheels it works out to 25mm.