There is this Erlang unit, for the number of simultaneous calls a telecommunication system can handle. https://en.wikipedia.org/wiki/Erlang_(unit) It's dimensionless, because it multiplies the rate that calls are initiated by the average length of a call: 'calls / second' by 'seconds / call'. Dimensionless.

But that makes little sense - we're measuring the number of simultaneous calls. It gets reflected in buffers, circuits, sockets, channels allocated, etc.

It would be better to consider 'call starts / second' as the rate at which calls are initiated, and the average 'call.seconds / call start', which when multiplies gives the more sensible unit 'call'.

Or simpler: just measure the average length in seconds. So we have so many 'calls / second' initiated, and the average length is so many 'seconds', which when multiplied again gives a unit of 'call'.