Description of inch vernier calipers
Two types of vernier inch calipers are available. One has 25 divisions on the vernier scale of the movable jaw, and the other type has 50 divisions. The 50-division scale is easier to read than the 25-division scale because there are fewer divisions and they are further apart.
The 25-Division Vernier Inch Caliper
The bar is graduated in exactly the same way as the sleeve of an inch micrometer. Each inch is divided into 40 equal divisions, each having a value of .025 in. Every fourth line representing 1/10 in. or .100 in. is numbered. The vernier scale on the movable jaw has 25 equal divisions, each having a value of .001 in. The 25 divisions on the vernier scale occupy the same spaces as 24 divisions on the bar; therefore, only one line on the vernier scale will line up exactly with a line on the bar at any one setting. To read a 25-division vernier, note the following numbers shown to the left of zero on the movable jaw:
:The last large numbered division on the bar to the left of the zero on the vernier scale represents whole inches.
:The small numbered divisions on the bar, between the inch and the zero on the bar, represent .100 in.
:The number of main scale divisions, between the last small numbered division and the zero on the movable jaw, represents .025in. each.
:To this total, add the number of thousandths (.001) indicated by the line on the vernier scale which coincides with a line on the bar.
The 50-division vernier inch caliper
Each line on the bar of the vernier represents .050 in. Every second line is numbered and represents .100 in. The vernier scale on the movable jaw has 50 equal divisions, each having a value of .001 in. The fifty divisions on the vernier scale occupy the same space as forty-nine divisions on the bar; therefore only only line of the vernier scale will line up exactly with a line on the bar at any setting. To read a 50-division vernier, note the following numbers to the left of the zero on the movable jaw:
:Inch increments shown by the large number on the bar
:Hundred thousandths (.100) increments shown by the small number on the bar
:Additional fifty thousandths (.050) increments to this total
:Add the number of thousandths (.001) indicated by a line on the vernier scale which exactly coincides with a line on the bar.