How do I use either or TSB2000B or MSO2024B to measure differential voltage?

How do I use either or TBS2000B or MSO2024B to measure differential voltage?

I am trying to look at an RS485 signal which requires looking at the differential voltage between RS485+ and RS485-.  It appears that both of these scope models may be capable of differential voltage measurements with the appropriate probes but I haven't found any guidance on what probes to use or how to perform the measurement.  I would appreciate any guidance on this.  Thanks!