Greenlee THH-100 Instruction Manual page 8

Distance to Spot Size
The distance to spot size is a ratio that provides the
appropriate distance to the target. The ratio is stated in a
nominal value for the focus distance, which is 750 mm (30")
from the unit. Use the illustration shown here or the decal on
the side of the unit to determine the distance-to-spot-size ratio
for each application.
The nominal distance-to-spot-size (D:S) ratio at the focus
point is 6:1.
D:S = 6:1 at Focus Point
133 @ 800
mm
83 @ 500
50 @ 300
5 @ 30
3.3 @ 20
2 @ 12
inch
Nominal Spot Diameter at 90% Energy
8