The other thing is that a stopwatch even if it was perfectly accurate is measuring average speed and not release velocity. The standard by which pitchers are compared is release velocity. Depending on spin, etc. two pitchers could have the same average velocities and different release velocities.
PG, You can change the distance on that but it still measures an average velocity.
My son was timed a couple times in the 40. He looked to start early the first time and looked to run faster the second time. His first time was pretty good for a young NFL running back. His second time was close to in line with where we think he probably is in the 60 these days and about .2 seconds slower than the first time.
I have to admit I'm not very good at judging velocities by eye. I was at a college camp over the weekend and the first pitcher looked like he was throwing hard. He was pretty consistently 90 on their gun. The second or third pitcher looked to me like he was low to mid 80s. He was high 80s and may have touched 90. Knowing some of this school's pitchers they are a school which goes after pitchers based on their ability to pitch and not just on velocity but they were using a gun.