advanced time calculations in Excel

Question

​ this snippet from my spreadsheet calculates an employee's time and their productivity during that time.

Not all employees work the same times, so is someone starts at a different time, their unique start time is entered into f8.

When its time to measure, A macro enters the time into f13. All of this math works fine. What I have been unable to solve is this problem:

If this employee is not measured at 11:00 (f13) but is measured at 12:09 (f17), meaning that f13 is blank, the total hours (f6) is blank. (delete the 11:00) in f13 to see what I mean) Why? Well, more specifically, why does e16 return a #value! error? F6 returns a 0 value because of the IFERROR formula.

So my question is, what is the formula that I need to enter into e16 and e20 (they are different) so that I dont get a #VALUE! error is there is no time in the time cell above it? I hope that this is clear.

I'm not aware of how to send a file, so I sent these screen shots. I hope that is ok. Thanks to all who spend time on this.

enter image description here

Answer 1

I'm going to be cheeky and add the problem here.

the function

TEXT(F13-B8,"h:mm") and all its uses where the expression produces a negative value.