HP 54645A User's And Service Manual page 140

To enter characters into the new label:
4
Press the Position softkey until the cursor position in the entry field
a
corresponds to the point where you want to replace a character.
Enter or delete a character.
b
To enter a character, use the Entry Knob to choose a character from
the character list. Then press the Copy softkey.
To insert a space, press the Insert Space softkey.
To delete the current character, press the Delete Character softkey.
Delete Character deletes the character under the cursor and moves
successive characters forward by one position.
Press the
5 Assign Label softkey.
The label is assigned to the selected channel.
Label display is automatically enabled when you enter the Define Labels
menu. Thus, if the labels were off, they are turned on while you define labels.
If you exit the Define Labels menu, and the labels were off before you
entered the menu, they are turned off when you exit.
Using Labels on the Mixed-Signal Oscilloscope
To define a new label
4-57