How do I know when to read a number as (for example) 241 or 24.1 off the navigation computer?
If you are talking about an E6B, you follow the same rules for your result as you followed for your inputs. If you used a factor of 10 for your inputs, you use a factor of 10 for your results. If all else fails, you use the common sense rule. For your particular calculations, does 241 make sense? Or, does 24.1 make sense?