Tektronix TriMode TDP7700 Series Technical Reference page 23

Theory of operation
The offset range limits apply to each side of the single-ended inputs. Due to this,
the common-mode and differential offset ranges are limited to the area shown in
the diamond-shaped graph below. When the maximum differential offset is
applied, the common-mode offset is restricted to 0V. Similarly, with the
maximum common-mode offset applied, the differential offset is constrained to
0V.
It is additionally possible to turn on an Autotracking function. In C-mode, the
autotracking function adjusts the offsets to null out the low-frequency differential
input seen by the probe amplifier, maximizing the common-mode dynamic range.
In D mode, the autotracking function adjusts the offsets to null out the low-
frequency common-mode input seen by the probe amplifier, maximizing the
differential dynamic range.
TDP7700 Series TriMode Probes Technical Reference 15