For measuring net height in the middle, one should bring a wood racket with them to the courts.
Keep your wood racket in a press so the proper net height is not compromised.
A wood racket with leather grip makes a classy measuring device (and conversation piece).
Hope this helps........
June 2012: Making a comeback after 15 years! Who's this guy Roger Federer?
PK Kinetic 7G, Bab 17g n-gut @ 50 & PK Q Tour 295, Wilson 17g n-gut @ 50