The UL is a test command that results in a UV scan being performed with an external lamp to cover the range 290 - 325 nm. Only slit #1 is used and the NiSO4+UG11 filter (position 242) is used for the full range of the scan. Note that the UG11 filter (position 50) is used on a MKIII instead. The zenith prism is rotated to the UV dome, FW#2 is set to the 1 position, FW#1 is set to the 3 position, the iris is opened, and the tracker is rotated to the sun. The operator is asked for lamp number, and lamp-diffuser separation, and the radiation intensity is measured in 1.5nm increments over the UVB range. Data is stored in a ULJJJYY.nnn file.