Cooking time rules.

There should be a guide on the outside of the ham telling you what temperature the inside needs to get to in order for it to be done. If not, it ought to have a guide for weight -> cooking time guide. Of course, that way is only a guideline since the specific geometries of the ham determine how long it takes for the inside to warm up.

http://www.cooksrecipes.com/tips/mea...ure-chart.html

That table should be useful, though.

Also, don't forget that meat cooks after you take it out of the oven, since there's still heat inside of the meat. Some of this will make its way to the inside of the meat heating it a few degrees past what it was when you took it out of the oven. Lower temperatures lead to a more even heating of the meat and higher temperatures will cook the outside fast while leaving the inside not as cooked (probably not what you'd want for a ham).

Jam it back in, in the dark.