DT in CMS

Drift Tubes are used in the Barrel where the Magnetic field is guided and almost fully trapped by the iron plates of the Magnet Yoke.
(...) The coordinate on the plane perpendicular to the wire is obtained with high precision from the time taken by the ionization electrons to migrate to the wire. This time (measured with a precision of 1ns), multiplied by the electron drift velocity in the gas, translates to the distance from the wire.

Note: 2-fold ambiguity on the hit (you only measure the distance from the wire, but you don't know if it was on the left or the right.)