Grid Offset
 

I would like to propose adding a "Grid Offset" or "Grid Origin" setting to the "Canvas: Grid" inspector, so that we can set the origin of the grid. Sometimes it is useful to be make the grid start from a particular spot on the page (for example, a margin boundary).

I hope you will see fit to add this feature to a future version of OmniGraffle. Thanks for reading my suggestion.

Although you can change the ruler origin when the rulers are visible, this doesn't affect the grid origin. A simple solution would be to make the grid respect the ruler origin.