Add elapsed time counter to scan (redis and HDF5)
ID10 asked to have the
dt (aka elapsed time) column stored as counter in both redis and HDF5.
It is superfluous information because we already store the timestamp and the scan start-time.
Since the timestamp is very abstract I propose we store the scan start-time and the elapsed time of each point instead.
If someone needs the timestamp of a point he/she can have it by
point_timestamp = scan_start_time + point_elapsed_time.