Locating the Center of the Rod – by JV

JV has become increasingly interesting in machining.  His godmother’s neighbor is a retired machinist and JV visited with him yesterday.  He was lent a high school shop manual.  He has begun reading it.

The first way to locate the center of the square.

1. put the work rod in the vise
2. lay the center square against the side of the rod near the end
3. put a ruler under the center square across the top of the rod
4. scribe lines along the ruler
   
5. move the ruler to the other side of the square and scribe lines
6. rotate the rod 90* in the center square
7. repeat steps two and three

The second way to locate the center of the rod is the hermaphrodite caliper.

1. put work in vice
2. adjust the caliper to half of the diameter of the work.
3. place the curved “leg” of the caliper on the side of the end of the rod and rotate.
4. scribe a quarter of a turn creating a semi-circle.
5. do this three more times rotating the piece 90* each time this creates a concave square.

I did not understand the third way.