Keysight U1251B Guia Del Usuario página 165

Performance Tests and Calibration 6
5 Use the editing keys and to step each character in the code.
6 Use and to select each character.
7 Set the code, same as the last 4 digits of the instrument's serial number.
8 Press (Save) to confirm the entry.
9 If the 4 digits entered are correct, the secondary display will show PASS.
Now you can use 1234 as the security code. If you want to enter a new security
code, see "To change the instrument calibration security code from the front
panel" on page 162. Make sure you record the new security code.
Keysight U1251B and U1252B User's and Service Guide 163