  We present in this work the calibration procedure and a performance study of
long scintillator bars used for the time-of-flight (TOF) measurement in the
HADES experiment. The digital front-end electronics installed at the TOF
detector required to develop novel calibration methods. The exceptional
performance of the spectrometer for particle identification and pointing
accuracy allows one to determine in great detail the response of scintillators
to minimum ionizing particles. A substantial position sensitivity of the
calibration parameters has been found, in particular for the signal time walk.
After including the position dependence, the timing accuracy for minimum
ionizing particles was improved from 190~ps to 135~ps for the shortest rods
(1475 mm) and to 165~ps for the longest (2356 mm). These results are in
accordance with the time degradation length of the scintillator bars, as
determined from previous measurements.
