Adding More Useful Tick Mark Labels to a Histogram
Abstract: Sometimes,
when drawing a histogram, the number of tick
labels do not match up with lines on the bars.
With a few minor calculations and specifying
a few more options on the ghist command, you
can easily make sure that the values encompassed
in each bar are clearly defined, regardless
of the number of bars of values in your data.
Products:
Statit
eQC, Statit
eServer, Statit
Custom QC
For example, take the follow commands used
to generate a Histogram chart:
getfile
"qc.wrk" /begin
ghist Temperature
It generates output like this:
The boundaries of the bars do not match up
exactly with the tick label marks. Users often
find this confusing as they try to determine
the frequency of their measurements within a
given range. Using a few quick calculations
and given a tick mark step value, we can find
out the number of bars needed to make these
match up. Try the following:
getfile
qc.wrk /be
##
Specify the step value here
#step = 5
##
Calculate number of bars necessary for specified
step value
$bars = int((max(Temperature)  min(Temperature))/
#step) + 1
##
Draw histogram
ghist Temperature /classes=$bars /step=#step
It generates output like this:
As you can see, the tick marks and labels now
line up directly with the edges of the histogram
bars. To increase the number of bars in this
example, simply lower the tick mark step value.
