Marking a bolt circle by stepping a divider round it accumulates error and the last hole never lands right. This gives the exact X and Y of every hole from the centre, so you set out with a rule or a DRO instead.
Notes
Coordinates beat stepping round
Stepping a divider means each hole inherits the error of the one before it. Coordinates are measured from a single origin, so no error accumulates and the last hole closes as well as the first.
The chord check
The chord is the straight-line distance between adjacent holes, equal to the PCD times the sine of 180 divided by the number of holes. Measure it on the finished part and you have an independent check on your setting out.
Finding an unknown PCD
On an existing flange, measure the chord between two adjacent holes and work backwards: PCD equals the chord divided by the sine of 180 over the hole count. That is more accurate than trying to measure across a circle where the centre is a hole.
What this does not do
It positions holes. It says nothing about hole size, edge distance, thread engagement or whether the pattern is strong enough for the load.