HI Hadi, The cool thing about the IDL language structure is that it isn't complicated in any way when it comes to making mathematical equations, be they for temperature or for calculating shear stresses in a metal beam. You didn't mention what your temperature equation was supposed to do so I can't give you an exact example of what your equation would look like. However, if you did a Google search for the Fahrenheit to Celsius conversion you would find this equation: Tc = (5/9)*(Tf-32) ...where Tc = temperature in degrees Celsius and Tf = temperature in degrees Fahrenheit That is the same equation you would use in IDL. If you have something more elaborate you could look in the IDL Help on 'mathematical operators' to check on the syntax of the equation. Hope that helps Ciao