radar guns are +/- one, so you could prob get it lowered to 87 if you want to decrease your fine a little, or you could possibly get the whole thing thrown out because he showed you the radar gun that said 88, then gave you a ticket for 89. cases get thrown out all the time for little discrepancies like that. you should at least get in touch with the county prosecutor and tell him about the radar gun and see what he says.
my first ticket was 24 over and it was right after they passed the law that said you lose your license for 24+ if you are under 21, so i called the county prosecutor and he lowered it to 23 and i plead no-lo and paid a fine.