Tracking force here means the downward force that the stylus exerts on the record, usually measured in grams. Also called, somewhat misleadingly, stylus pressure. Actual pressure exerted by the stylus, given the tiny contact area involved, is around 20 tons (yes, tons) per square inch.
Dedicated gauges are available from around £5 upwards.
A quick 3.25g can be added (3.35g if you want to stay in period) by taping a 5p (6d) coin to the headshell. This is a typical period modification