All:
I can't help myself. I like PG's thoughts on "seeing" the throw and backing it up with what the radar says. My old coach used to say, "I can tell a baseball player by the way he walks off the bus." I can apply this same thought to PG's description of judging arm strength. "He can tell good arm strength just by watching." The radar just verifies.
That said, gents, I'm old school. Back when I played, Old Buzzy Keller used to stand us at 250 feet from home plate. He'd get out the old stop watch and time your thrown from that 250 until it crossed home plate. Guess what? 3.0 seconds or better...decent arm. We had guys at 2.5 & 2.4. Cannon...BTW. What does that relate to? Carry plus velocity. Now that was easy to see. No radar.