HP 61010A Owner's Manual page 22

Step 7
- The input display changed to 65535, which is the
unsigned representation for all 16 input bits being high.
Now point to and select the S3 arrow to change the
base to BINARY {see Figure 2-8). Each time you point to
and select the S3 arrow, the top choice in the list rolls
down into the center position. The choice at the bottom of
the list rolls around until it appears at the top of the list
again. (The choice that is currently active stays bright as it
rolls around in the list).
STATUS: front Panel Control Mode
Figure 2-8. Change the Base to Binary
2*10 Trying Out Your instrument