I could not find on PhaseOne website, the shift information for the XT. But giving only one number "24mm" may suggest, at least to Linhof Techno and Silvestri Flexicam users, that this means -/+ 24mm.
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Linhof Techno (
https://bit.ly/2mxYXw8)
Front standard:
Horizontal parallel shift: 10 mm left, 10 mm right
Vertical parallel shift: 20 mm nach oben [sic]
...
Rear standard:
Vertical parallel shift: 20 mm up, 20 mm down
Silvestri Flexicam (
https://bit.ly/2me6qAe)
Vertical shift 23 + 23mm
Horizontal shift 15 + 15mm
P.S. Now I found it at P1's website (
https://bit.ly/2mzR0Xf). I stand corrected, it's clear that it's -/+ 12mm
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Horizontal dial
12mm shift to the left
12mm shift to the right
Vertical dial
12mm shift up
12mm shift down