I use “set grid origin” for this type of thing.
- Start in mm, draw the board outline.
- Move cursor to top left of board outline and press spacebar
- Select “grid origin” and click at relative coord (22,22)
- now you can switch to inch, and the grid is centred on the board
- you can reset the grid origin to the top left of the 0.1" matrix
You could do it the other way. i.e.
- start in inches
- draw the grid of holes in inches
- set the grid origin to the centre
- switch to mm
- press space at the origin
- draw board outline (-22,-22) to (22,22) mm