TB/TD tacho signal. What voltage & waveform?

Does anyone know what voltage and waveform (AC or pulse DC) the TB and TD tacho signals are? And hows many pulses per engine revolution? A screen shot of an oscilloscope would be handy if anyone has one.

Alternatively, does anyone know if an Autometer tach adaptor will control either TB or TD factory tacho's?GQ TB/TD tacho signal. What voltage & waveform?

Mudnut may know he was looking into an osilliscope last week

Sorry, bloke, I've just only ordered a handheld oscilloscope. It will take a week or two to get here. The only other info I have is the link given me for the speedo signal. I will post info as I get it.