Column histogram with +/- 50

Hello. I'm trying to create a column based histogram with 50 as the centering point. As an example, if you normally had one column of negative numbers and one of positive numbers you could create a histogram with 0 as the center point and the positive numbers plotted above and the negative numbers plotted below. How might I accomplish that when all numbers are positive? I'd like 50 to be the center line and numbers 51-100 plotted above and numbers 49-0 plotted below.

Here is an example.

Thanks!

http://img163.imageshack.us/img163/204/histogram.png

Thanks, Andy. All that seems to do is flip the chart upside down...

Cross at 0:
http://img848.imageshack.us/img848/6825/xcross0.png

Cross at 50:
http://img607.imageshack.us/img607/4219/xcross50.png

Did I enter it incorrectly?
http://img26.imageshack.us/img26/5525/xcrossscreen.png

All the best,
Morgan

Beautiful! Thanks a ton for your help.