Each cycle represents one order of magnitude greater than the one below it.
Values in each cycle are 10x greater than those in the preceding line.
Useful when you have to fit a wide range of values on a single graph.

Interpretation:

Sloping straight line - constant rate (not amount) of increase or decrease in value.
Horizontal line - no change.
Slope of line indicates rate of increase or decrease.
Two or more lines following parallel paths show identical rates of change.