Linear data has a constant scale that applies to the axis. i.e. moving 1 inch in
a particular direction always changes the x or y value by a constant amount. This scanned
image has linear x and y axes. Click here for generic instructions.
Log data has axes in a logarithmic scale. Moving in a particular direction by 1
inch does not always change the x or y value by a constant, however the change in log(x)
or log(y) IS constant. Log axis labels can be scientific (x-axis) or numeric (y-axis), as
shown below. Click here for generic instructions.
Dates are common graph types for stock market charts. Below is a graph showing
Dell share prices, as quoted by Yahoo! It has a date-format x-axis, and a log y-axis.
Click here for generic instructions.
Time charts are common for data acquisition, intra-day stock charts and
scheduling graphs. Below is a generic candle chart of intra-day option prices. This chart
has a time x-axis, and a linear y-axis. Click here for generic
Point to point measurements are useful for sizing features on pictures. The
following picture shows grains inside a superalloy at high magnification. Width and length
measurements of the needle shaped grains would be a point-to-point measurement
application. A scale bar, or some reference feature is required if exact dimensions are
Angle measurements can be made on any photo. The image below shows a
calibration-test image. Angle measurements do not require scale bars.