To start the checkbox sequence - select “PAT” from the home screen of the Apollo 600, then F3 (PAT with a hand symbol) and then F3 again (Ohm sign with a blue info sign). At this point you will receive a message asking you to connect the mains lead (to the black socket) and the IEC lead between the EUT socket and IEC socket on the tester (note you do not connect the checkbox at this point - you check the IEC lead first). After successfully completing the IEC lead test, connect the checkbox to the IEC lead and the red test probe, then select F3 and F5 to save. The checkbox test will continue until completion where you should see a message confirming the outcome. Regarding the checkbox interval, this can be changed but this is at your discretion, you should consider a risk assessment. To alter the interval, select “PAT” from the home screen of the Apollo 600, then F4 (crossed screwdriver / hammer), then F3 and at the bottom of the second screen use the blue arrow keys to alter the interval – select F4 to save on exit.