I use the Audio Additives Stylus Force Gauge. Relatively inexpensive, extremely accurate and easy to use. I also still have and will never part with my old trusty Shure SFG-2 that I bought in the 70s. It's old school (i.e. not digital; all counterbalance mechanical), reasonably accurate and will never fail. I keep it on hand in case the digital conks out and I have to order a new one.
