Beta 1760/IR1000 Manual Instrucciones De Uso página 27

5. Distance & Spot Size
As the distance (D) from the object increases, the spot size (S) of the
area measured by the unit becomes larger. The relationship between
distance and spot
size for each unit is listed below. The focal point for each unit is 914mm
(36"). Thespot sizes indicate 90% encircled energy.