How do I use the USAF resolution target?

USAF resolution targets consist of bars organized in groups and elements. Each group consists of six elements (i.e. elements 1-6) and each element is composed of 3 horizontal and 3 vertical equally spaced bars. Each element within a group corresponds to an associated resolution, based on the bar width/space. The resolution of an imaging system is defined by the group and element just before the black and white bars start blending together.

Note: Although the test yields precise resolution values, this is a qualitative test which depends on the user's definition of acceptable blur. The vertical bars are used to calculate horizontal resolution and the horizontal bars are used to calculate vertical resolution. One line pair equals one black and one white bar.