W
2y
2y
! 2y $
= measured =
#"
&%
2m measured
13 ' 1
yaverage .
Note-If you count correctly (i.e., symmetrically) there are an odd number of tick-marks. Thus, you must subtract
zeroth order to determine average size of each tick mark.
This is the same as saying that a ruler that measures from 0 to 12 inches has 13 tick marks (since zero is counted)
and thus each equal interval (called yaverage ) is
yaverage =
12 inches
= 1 inch/division
(13 ! 1) divisions