Negative Points for Attendance?

[jherring]

I've set up my class with a 100 points possible final grade. My attendance policy is -2 pts for every unexcused absence (on the random days that I take roll). 

I can't seem to find a way to set up Attendance to subtract 2 points from the final grade for every absence. I'm only taking roll on random days, so one semester I may have 12 attendance checks and the next I may have 15.   At present I've got custom column with 0 points towards for the final and will currently just put in -2, -4, -6 for the absences.  I like the idea that the students can see that they were absent on said days. 

Any thoughts or suggestions would be appreciated. 

[kona]

 @jherring , I think the way you have it setup is probably the best. The only other thing I can think of is it add a comment with the date for every day a student misses.