InfoPath Dev

Please... I did the exact formula you gave me, but it didn't work. The field2 was still blank, it did not change to the alphabet. I marked field2 as read only and i followed the format, the condition, rule type was set to action, action too was set to "set field's value...jet it didnt work. Please this is the scenario; ...

I am a newbie, and i am designing a form with infopath that contains student academic records (scores). I want to know the actual syntax that can calculate a grading score automatically, such as 100 - 90% will apear 'A'. Lets say, i have 2 fields, field1 and field2. If field1 contains a value of 90 - 100%, then field2 should appear ...