while (ch1 < ch2 && currentChamber > ch2 + 1) {
// extrapolation to the missing chamber
currentChamber--;
if (!AliMUONTrackExtrap::ExtrapToZCov(&extrapTrackParamAtCh, AliMUONConstants::DefaultChamberZ(currentChamber),
GetRecoParam()->UseSmoother())) return kFALSE;
// add MCS effect
while (ch1 < ch2 && currentChamber > ch2 + 1) {
// extrapolation to the missing chamber
currentChamber--;
if (!AliMUONTrackExtrap::ExtrapToZCov(&extrapTrackParamAtCh, AliMUONConstants::DefaultChamberZ(currentChamber),
GetRecoParam()->UseSmoother())) return kFALSE;
// add MCS effect