TDS2024 Pk-Pk Measurement
The signal generator is expecting to be run into a 50 ohm impedance - if you did that the voltage would drop to 1 Vp-p: -



See the little red square I've added - inside that square is written 50 ohm.

From the manual it says this: -


  The Agilent 33210A has a fixed series output impedance of 50 ohms


See also this page for confirmation. BTW you can rely on the 2Vp-p providing you run the output into a high impedance. With a load of (say) 1 kohm, the output will be 1.905 Vp-p. With a 10 k load the output will be 1.990 Vp-p and, all the time the display will indicate 1 Vp-p.