I also would have thought that this could create stress moving them about a lot, also in the shade its hard to tell how much light they are getting.
When i first started growing i bought this cheap anologue ph meter that also measures lumens/watts and i tested it once when the sun was shining, not a cloud in the sky, so i started playing around with it and in the shade they was getting the equivalent off around a 250watt light so i scrapped that idea, and in the sun the dial was off the charts so as the others have said it would be wise to train them first.
this is the instrument i use (its useless really apart from the light measurer)
h**p://cgi.ebay.co.uk/SOIL-PH-LIGHT-MOISTURE-METER-garden-plant-greenhouse-UK_W0QQitemZ160327112730QQcmdZViewItemQQptZUK_Home_Garden_GardenEquipment_HandTools_SM?hash=item160327112730&_trksid=p3286.c0.m14&_trkparms=72%3A1686%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318