i need to keep a track of the number of hours of travel and time spent onsite for service work.

So far its been a simple matter of creating a start datetime field and an end datetime field with a drop down to pick the correct activity, is there a way however to automatically calculate the difference between the two and present the result in another field?

i can see that you can create a field and then have this calculated but what is the formula for such a field?

originally i thought this formula would be ok "subtract($start_time_c,$end_time_c)" however as the fields are not a number it gives an error message.

I fixed it with trial and error

divide(divide(subtract(number(timestamp($end_time_c)),number(timestamp($start_time_c))),60),60)

then just by creating the field as a decimal type field.

still not the best solution which should be the ability to show this in true time format 00:00:00