HP 54710A User's Reference Manual page 39

How the Oscilloscope Works
Choosing Probes
The resistance of the probe to ground forms a divider network with the
source resistance of the circuit under test. This reduces the signal amplitude
and the dc offset. For example, if the probe's resistance is 9 times the
Thevenin output resistance of the circuit under test, the amplitude is
reduced by about 10 percent. See figure 1-9. The frequency-independent
amplitude errors and dc offset errors introduced by probe resistive loading
are approximately proportional to the ratio of the probe's resistance to
ground and the equivalent output resistance of the circuit under test.
Figure 1-9
Reduced amplitude and dc offset caused by probe loading
1–22