ZIPP valve length

[Feanor]

When I bought my ZIPP Super-9 Clincher rear disc wheel, it came supplied with a tube.

I didn't measure the length of the valve before installing it.
So now I want to have a couple of spares, and I'm not sure what length they are.
It can't be too short, or too long, in order to sit correctly within the cutout.
I really don't want to take the tube out to measure it.
The cutout in the disc is quite close to the rim, and measuring externally I reckon it's a regular 42mm valve.

Can anyone confirm from actual personal knowledge / experience?

[zigzag]

rim bed (the deepest part) is usually level or +/- a couple of mm from the inner edge of brake track, so i'd measure it from there; otherwise remove the inner tube for certainty.