USB Digitil microscope advice

The cheaper that the optics are, the harder to use.

Good luck finding a useful one.

Either to look at a profile of a cartridge or to use during set up of SRA, you will need to get a decent microscope. The cheapo's on Ebay are a waste of money - I eventually threw my $10 made in China microscope away.  I bought a used dino-lite microscope model AM4515ZT (retails for ~$750) and have only been using it to look at profiles of cartridges. I will say even that also requires a lot of patience and skill. To measure/set SRA, I would need a tripod/stand of sorts (based on my setup) and have not ventured that far into the pursuit.  If you're serious about wanting to use a microscope to set up a cartridge, the Wallyscope looks interesting and costs ~$1250.  Good luck.

I own a Wallyscope and it is certainly a cut above whatever you are going to find on the net. The problem is positioning and focusing the scope in a horizontal position. With a regular USB scope it will take a lot of cleverness. The Wallyscope stage makes it much easier and it has much higher magnification so you can evaluate stylus wear.

Modern cartridges are very well made. I highly suggest the WallyReference tool. It will line up most cartridges perfectly.