datetime derivations
- datetime from start/stop - symbol - description - unit - variable name - \(t\) - datetime (mid point) - \(s\) since 2000-01-01 - datetime {time} - \(t_{e}\) - datetime stop - \(s\) since 2000-01-01 - datetime_stop {time} - \(t_{s}\) - datetime start - \(s\) since 2000-01-01 - datetime_start {time} \[t = \frac{t_{s} + t_{e}}{2}\]