Tapered guages are narrow enough at the ends to slip between the cam guides to reach the valve buckets and measure the gapNon tapered guages are too wide at the business end to get to the buckets.
Thats what I thought he meant, a stepped gauge.I used to have a spark plug gap measure that looked something like your sketch.
Jewellers have something like that, but, much bigger for measuring your ring
Bolt this to your bench , sit your ring on it and swing on the leaver