Thank you very much for your help! The formula now looks like this...
If not IsNull({tblSOLogs.StartDateTime}) and not IsNull({tblSOLogs.EndDateTime}) Then
NumberVar logDiff := DateDiff('n',{tblSOLogs.StartDateTime},{tblSOLogs.EndDateTime});
NumberVar hours := logDiff \ 60;
NumberVar minutes := logDiff mod 60
I inserted the formula into the report and it's not calculating correctly and am not sure where I've gone wrong, sample output below:
Mark D - SO - Log Reason - Start Date - End Date - Diff
112 Shop 2-4-13 7:55 2-4-13 9:15 20:00
115 Travel 2-4-13 9:15 2-4-13 10:15 0:00
118 Labor 2-4-13 10:15 2-4-13 15:00 45:00