"Tennis: What's the secret of power and speed in serving?
Goran: Whenever I try to hit hard, I serve weak. When I don't worry about speed, but about the serve quality, then I serve faster. Anyway, for a fast serve you need to be relaxed- your hand needs to be loose, you must not force anything. And the speed also depends on the gun
position. If the gun catches your serve at an angle, it appears slower than it is. Sometimes I feel I've hit a fast one, and it's only 110 m.p.h. Other times the serve doesn't feel so fast, and it turns out to be 130 m.p.h. The angle has a lot to do with it."
This was 1995. The guns were measuring the ball as they approached the net, instead of the contact point.
Modern guns are not a single "radar gun pointing at the serve", but a combination of several measurement devices.
T serves on 90s guns measured the highest, while body serves had less OOMPH on them, and wide serves (Goran's bread and butter) measured the lowest.
I have at least, 40 or 50 Goran matches on DVD, and must have seen at least 120, and lemme tell you, his fastest serves are JUST AS FAST as Roddick's cannonballs.
In fact, I watched a youtube video not so long ago with a HUGE first serve by Ivanisevic in 1996. I mean, HUGE. Looked no slower than Roddick's 150. The gun clocked 128 mph. It was a flat serve outwide on the deuce side. I'll try to find the vid and post it.