Numbers will not keep format, even when applied to cells with no data

joerockbottom wrote:

I'm trying to get the cells to be formatted for Duration. No time. No date, just hours minutes. I apply that to empty cells, but then it keeps reverting to "Automatic." I have two columns, trying to format both for Duration so I can subtract one from the other. But when I try to subtract one from the other it says I can't subtract a number from a date format.

As you have probably discovered Numbers and Excel handle date-time differently.

Excel uses a serial number.

Numbers uses a date-time string. Also, Numbers has a Duration data type that Excel does not have.

To enter a Duration (a span of time) in Numbers you can't use special notation that doesn't seem to be very well documented.

To enter 10 hours 5 minutes you would type 10h5m. You can then format that as 10:05 if you want under the Cell pane Data Format pane. But use 10h5m to enter.

You can subtract a Number from a Date-Time value. That gives you a Duration. Here's a table showing that and subtraction of a Duration from a Duration giving a Duration, and a Date-Time from a Date-Time, also giving a Duration.

SG

If you format a cell as duration but type something into the cell that is not a duration, the cell will revert to "automatic". Is that what is going on? Can you give an example of what you are typing into these cells?

What is it you are trying to do? Subtract two times of day to get a duration or subtract two durations to get their difference?