Draw a cross and write a 7 on the top right of the cross, which is the second molar on the left and the seventh tooth on the left. The second premolar in the right mandible is the fifth tooth in the lower right, so it is enough to write a 5 in the lower left of the cross. Because we are face to face with the patient, and the direction of recording is just opposite to the patient's own left and right, so we should write like this when recording.