A verneir caliper is more accurate & the prefered measurement device for anyone qualified to carry CFTS inspections.
Fork gauges are ok for a quick check.
you need to buy a fork gauge, promptly
In the USA, we say that if a fork has worn 10% of it's width, it has lost 1/2 of it's load bearing capacity.
We also have a requirement for annual inspection of the lifting devices (including forks and chains) and replacement, [no further use] if worn 10%, wear is usually in the heel of the fork where it scruffs the ground.