XML rolling numbers formula to get numbers

subject title doesn't explain this verywelll...i am making a gauge that has rolling numbers in it up to the 100's column.I made a similiar gauge to make a rolling number altimeter by robbing the code from the 747 cab file...I am now trying to adapt the code to make the gauge work in the 1's 10's and 100's column but i am stuck on this strange backwards maths and the whole modulus of a number bit.i need the gauge to show also a minus sign when beloe zero. I know this will be another "rolling number" strip with just a blank and a - drawn in... but can anyone provide the formulas...the gauge will look like thisXXXor-xxxwhere the xxx is the number. ( so i could have -014)