To find 7/8 on a ruler, count seven 1/8 marks from one inch to the next. Or fourteen 1/16 marks from inch to inch.
One thing I made sure of was my kids could read a ruler, down to the 1/64 inch, and know the gauge numbers sizes. It's something not taught in most schools anymore. I started teaching my grandbaby how to read a ruler when she started counting. It's a skill they will not forget.