The MEAS:MEAS<X> commands refer to the on screen measurements. The <x> here indicates which measurement you are working with however, not which channel to make the measurement on. So, if I wanted to setup the on screen measurements for CH2 amplitude, as the only on screen measurement, then I would do the following:
-trigger the scope here and make sure you have a good acquisition
One trap that you can fall into is that the MEASU:MEAS commands are updated periodically by the scope. If you trigger the scope, then immediately query the MEASU:MEAS1:VALUE?, it might still have and return the measured value from the last acquisition. If you use the MEASU:IMM commands instead, it will calculate the value on the fly for you, and return the results so that you know it is from the current acquisition. There is only 1 MEAS;IMM slot though, so if you need to do several measurements, you will have to change the MEAS:IMM:TYPE between each query.