Hi there, If I do the following: IDL>JE=6.7142891D IDL>JE1=6.7142891D IDL>if (je ne je1) then print, "not equal" IDL> It works correctly. So, the question is, how did you defined those two variables? Remember that the type double contains many more decimal places than that. What you see when you say "help, je" is just the first 7 decimal places. so it is possible that both variables are not "exactly" the same. Cheers, fernando

Ah, welcome to the realm of computer science! You are about to learn how numbers are represented on computers. (Not to give anything away, but the answer is "not too well".) Here is an article that is well-thumbed by many a scientist before you: http://www.idlcoyote.com/math_tips/sk... Be sure you follow all the links. I can assure you, it will be worth your time. :-) Here are some other articles that may also be of interest to you: http://www.idlcoyote.com/..._tips/razoredge.html http://www.idlcoyote.com/math_tips/double.html http://www.idlcoyote.com/...h_tips/storenum.html http://www.idlcoyote.com/math_tips/oneplus.html

You might also be interested in the Coyote Library routine, Floats_Equal: http://www.idlcoyote.com/...ams/floats_equal.pro