sentences:  This study observed the effect of a change in tempo on the number and mean duration of pauses; thus, now using the letters to represent proportional changes in values,
  
  nd = 1⁄t, where n is the proportional change in pause number, d is the proportional change in their mean duration, and t is the proportional change in tempo.This expression describes a number–duration curve, in which the number and mean duration of pauses form a hyperbolic relationship (since neither n nor d ever reaches zero).The curve represents the range of possible ratios for using these variables to adapt to a change in tempo.