# datetime length derivations

1. datetime length from start/stop

   symbol | description | unit | variable name
   --- | --- | --- | ---
   \(t_{e}\) | datetime stop | \(s\) since 2000-01-01 | datetime_stop {:}
   \(t_{s}\) | datetime start | \(s\) since 2000-01-01 | datetime_start {:}
   \(\Delta t\) | time duration | \(s\) | datetime_length {:}

   The pattern : for the dimensions can represent {time}, or no dimension at all.

   \[\Delta t = t_{s} - t_{e}\]