Just turned 59 and still taking my glasses off (or lookin' over the top of them!)
The vernier scale is a method of getting to a finer degree of measurement. For an engineering vernier caliper scale, the graduations on the sliding part will be tenths of an inch and the vernier scale will refine that to hundreths (10 lines). For a fractional (architectural) scale, there will be probably 8 lines for the inch scale and the sliding portion of the caliper will be in 16ths of an inch (giving a 128th inch meaurement)
To read the vernier scale, first notice where the first line to the left lines up with the sliding part. If it lines up dead on, thats the measurement. If it is to the right of the nearest 16th, look to see which of the lines to the right align.
Example: Using a fractional vernier caliper: You measure a piece of "3/4" plywood, and the first line lines up halfway between 11/16ths and 3/4. If you count from the left on the vernier lines from the first line you will see that the 4th of the eight lines lines up exactly with one of the lines on the sliding scale (it doesn't matter which one, only that it lines up exactly) This means that in addition to the 11/16ths (nearest line to the left of the first line) you have an additional four 128ths (1/16th inital graduation times the 8 lines) or 1/32" additional width, giving you 23/32nds inch width.
Also, the inside and outside calipers are aligned, so if you measure your plywood (outside calipers) those same calipers will set your dado, and the opposite side (Inside calipers) will measure your dado cut (not allowing for glue clearance)
Hope this helps and doesn't confuse
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