Interpreting AU intensity confusion for values between 0 and 1

[ccma1]

As described in the documentation, For intensity of AU 1 the column AU01_r in the output file would range from 0 (not present), 1 (present at minimum intensity), 5 (present at maximum intensity), with continuous values in between.

What does a value of 0.5 for example represent? If 1 is present at minimum intensity, does anything below 1 mean not present?

Thanks