Line-group tests have proven themselves in determining the visual resolution values. According to the system being proved, these tests are obtainable in various spatial frequency ranges and in different steps.

For the testing of intensifying screens, tests are adequate whose line groups are arranged in only one direction: system errors in various directions are not to be expected, since the tests are laid directly on the cassette, directional-dependent errors of geometry do not have an effect.

For image-transmission systems in which, because of the specific imaging errors different resolution values are to be expected in the tangential and meridional direction (for example in the I.I. systems), it is advisable to use tests with line groups which lie close to one another and which are orientated perpendicular to one another.

To avoid false readings due to the so-called pseudo-sharpness, care must be taken that the recognizable number of test-group bars in the image agrees with that of the test. The besom test with its continuously varying spatial frequency represents a special form of the group test. It advantage lies, above all, in the certain avoidance of reading errors as a consequence of pseudo- sharpness.

When using a scattered radiation grid, it must be taken into account that the line-groups are arranged, if possible, at an angle to the strips of the secondary radiation grid which is less than 45°, in order to avoid moire effects.