Jeff wrote:
There is an apocryphal story that 50 ohms started out as a common impedance
for coax because that happened to be the number that came out using common
British copper pipe sizes.

The research I've done indicates that the old British pipe sizes
(1/2",. 3/4", 1") specified internal dimensions, while the new pipe
sizes use external dimensions and a wall thickness. Did the story take
into account this change in convention?

Zack Lau W1VT