You need a pocket mirror, a laser pointer and a counter. Then measure both the up-down time (or distance) and the down-up time (or distance). The two are different.
This means, taking light-radar as a reliable measuring device, that the two measured heights are different. As far as I know, the experiment has never been done in spite of its simplicity.
Why is it worth doing? This “V-Lambda” experiment can also be called “WM” experiment, with the two letters printed on top of each other. You then get XXXX. Very regularly, no shifts. That is, upper and lower time intervals interlock even though being different.
You can do the same experiment between earth and a neutron star (provided a mirror can be deposited on its surface). Then the two time intervals that interlock differ by a factor of about 2.