sentences:  The Hollomon parameter itself is unitless and realistic numeric values vary between 15 and 21.
  
  where "T" is in kilokelvins, "t" is in hours, and "C" is the same as above.Holloman and Jaffe determined the value of "C" experimentally by plotting hardness versus tempering time for a series of tempering temperatures of interest and interpolating the data to obtain the time necessary to yield a number of different hardness values.This work was based on six different heats of plain carbon steels with carbon contents varying from 0.35%–1.15%.