If you want to compute time values use the ‘T’, ‘t’, or ‘U’ flag, either in Calc formulas or Elisp formulas:
| Task 1 | Task 2 | Total | |---------+----------+----------| | 2:12 | 1:47 | 03:59:00 | | 2:12 | 1:47 | 03:59 | | 3:02:20 | -2:07:00 | 0.92 | #+TBLFM: @2$3=$1+$2;T::@3$3=$1+$2;U::@4$3=$1+$2;t
Input duration values must be of the form ‘HH:MM[:SS]’, where seconds
are optional. With the ‘T’ flag, computed durations are displayed as
‘HH:MM:SS’ (see the first formula above). With the ‘U’ flag, seconds
are omitted so that the result is only ‘HH:MM’ (see second formula
above). Zero-padding of the hours field depends upon the value of the
variable org-table-duration-hour-zero-padding.
With the ‘t’ flag, computed durations are displayed according to the
value of the option org-table-duration-custom-format, which defaults
to hours and displays the result as a fraction of hours (see the
third formula in the example above).
Negative duration values can be manipulated as well, and integers are considered as seconds in addition and subtraction.