Looks like this isn't possible, I get an input not in correct format exception. I feel like the final result of a calculation should be allowed to return a string...
Is there any way to return a string from the result of a formula or will the UltraCalcManager always attempt to cast the result to a number? I'm trying to give my users the most complete coverage when it comes to creating their own reports by creating custom columns and one such request was to display certain text depending on the value of another column. As it is right now I have to implement this on the InitializeRow event whereas I'd like the end-user to have this functionality.
I'm still a little unclear on what you are trying to do. It is certainly possible to have a formula return a string. But it depends on the formula and what control is displaying the results. If the formula returns a number, it will usually be returned as a double. But there are certainly formulas and functions that return strings.
There's a function in Excel called Text which converts a number to a string, but it looks like there is no such function in CalcManager. But you could create your own custom function for this. It would be pretty simple.