Poor mans lathe DRO's

[Saltfever]

. . . If you're going to check a micrometer for accuracy, it's important to use a set of gage blocks that cause the spindle to seat at different orientations so drunken thread errors will be noticed. The preferred set for inch micrometers is: 0.105, 0.210, 0.315, 0.420, 0.500, 0.605, 0.710, 0.815, 0.920, 1.000 . . . .

Marv, I notice your preferred increment is 0.105" each time. On a typical 40 thread mic that would be 4.2 threads. Anything special about 4.2 threads every time?