This makes them more accurate, but typically results in slower times. Our 40s were always hand-timed, and therefore faster (sometimes by more than a tenth of a second). At one point, a strength and conditioning program offered a free combine to our team - it turned out to be an event that allowed them to pitch their program to us, but we all went. Almost everyone on the team (myself included) freaked out when we saw our 40 times. They were using a laser system, and we were significantly slower than we had been the week before, timed with stopwatches.
I'm guessing that Linton's 40 will be hand-timed. 4.9 with a stopwatch shouldn't be an issue