You should call or email aeroforce and ask them what OBD II parameter they are polling for knock and the units they are displaying. There are a couple/few possibilities and you may have been comparing apples to oranges. Were you polling both short term and long term with the Diablo? (I'm assuming the Neon reports both of those? It may not have long term, I don't know). There also could have been problems if you had them both hooked up at the same time. OBD II doesn't support that. For speed and accuracy most any scan gauge would be the same. Accuracy: The scan gauge requests a parameter and the response comes back with a number it in. The scan gauge displays the number. It's possible to misinterpret the units but almost impossible to screw up accuracy in the gauge. For example, the ECU reports temp in celcius and the scan gauge displays that number in fahrenheit. Speed: The OBD II spec says you can only have 1 outstanding request at a time. So the gauge sends a request and waits for a response. Once you get a response (or time out -- it's a relatively long timeout) then you can send the next request. Could be for the same parameter or the next one in the list if you're scanning a number of them. Not all parameters will have the same response time. Some parameter values the ECU will have handy, some it will query other modules for, and some are calculated when the request is received (maybe from multiple other parameters that may or may not be available at the time). Once the scangauge gets the response it doesn't take much to put it on the display so speed is going to be more a function of the ECU and the diagnostic port bus speed.
