Knock meter

What knock meter would you buy and how are they set up.

It's really dependent on your budget. For a modestly priced option I'd go for the Link G4+ Knock Block. These are audio only and you simply bolt a knock sensor to the block and then listen using ear buds. For a more advanced tool I'd suggest the Plex Knock Monitor. This has the same audio input however it has a lot more adjustability in the filtering than the Link unit. The Plex also has some advanced graphical display options and can offer individual cylinder knock detection.