Speeding, but officer cited incorrect speed

I was going 8 miles per hour over the highway speed limit according to my speedometer (I had it on cruise control at this speed). I was speeding, but the officer said he clocked me going 12 miles per hour over the speed limit. 87 in a 75 according to the officer and this is what he cited me for. I should have kept my mouth shut and denied speeding altogether, but I didn't. Even knowing that I had cruise control on at 8 over he still cited me 12 over. Can I get out of the ticket because he cited me for the incorrect speed?

Also, he didn't sign the bottom of the ticket where it says, "I hereby certify service upon the defendant personally on the ___day of ___ 20____." Doesn't he need to sign the bottom of the citation for it to be valid? Can I get out of the ticket for this reason?

The court will correct any errors or ommission normally.

but you can argue the speed issue.

See also WORLDLawDirect - Fighting a speeding ticket