Would be interesting to see if any of the probes survive 50 years in space. More impressive if V1 continues to transmit beyond 1 light day. That would be June 2028.
So the transmission distance with respect to the rotation of the planet the probe was launched from at the time it was launched. I suppose that is more sophisticated than a unit which is somehow derived from the width of a horse's ass.
I'm thinking if the metric system was invented today, distance would be based on a light second somehow.