HP 61010A Owner's Manual page 15

As shown in Figure 2-1, your Digital I/O places two labels
in the System View Window list; one for the Digital Input
and one for the Digital Output. DIG.OUT.Ol is the factory
default label for the Digital Output. The letter D after the
label indicates that the output is disabled at this time. The
present output value is displayed in the line directly below
the label in the System View Window. This value can be
displayed in decimal (DEC), octal (OCT), or hexadecimal
(HEX) format. Binary values are displayed in octal format.
If you have more than one Digital I/O connected to your
interface, each additional Digital Output will be assigned a
sequentially numbered default label (i.e. DIG.OUT.02,
DIG.OUT.03, etc).
Trying Out Your Instrument 2-3