Measurement values are marked with ”>” if overflow occurred somewhere in the signal processing chain for a certain channel. This usually (but not always) means that the instrument registered at least one measurement value outside the measurement system’s measurement range.
A signal that e.g contains a short-term peak or a large DC offset can result in overflow internally even when the instrument reports relatively low levels.
For instruments with software version r5d or older, overflow on one channel means that the measurement values are marked with ”>” on all of the instrument’s channels.