stay away from the ebay crap unless known brand, I started with one and was a pain to wire up and never that accurate, I went and bought a jaycar digital kit, pics here:
i got the speco in mine. Easy as to wire up and works a treat plus its not a massive monstor tach that looks like ****. So highly recommended this side.
but bro, a tiny litl tacko wil not pik up da chikz da way a monsta tacko duz bro!!!
lik dey cum wiv a mad shift lite and evryfing so uz kno dat i meen biznez at da litez cuz1!!