You don’t need a variable in simpleFunction (see this post) For simpleFunction, you can put more variables, so if you wanted to do an average rounded to two places, you might use this code:
Note that cellContent takes a string, and simpleFunction returns a number. Keeping track of where you need numbers vs. strings vs. LaTeX is the tricky part. Looking at lots of examples of other code can help there.
The function \abs() is a predefined LaTeX function. So is the \round( , ) used here, and the \frac{ }{ } used at the link. You can see examples of LaTeX symbols here.