with additional sensors rather than tying into sensors the ECU is already obtaining data for. Trying to keep the setup as compact and free of cables tho... a combined device approach would need a second bluetooth-RS232 adapter (at $75 a pop, it adds up.. :-/ Or one could use the built in serial port on the PDA - cheaper, but have less mobility (for times when you may want to see sensor information while you're hovering over the engine bay)..
The ZEM uses the Labjack to obtain MAS and RPM info that is used for the real time trace of the fuel and timing maps. I agree that it isn't as accurate as what you could do with the OBD data but while we are only talking a few percent, it doesn't make a difference in practice as you are virtually never just making a single-cell change in the maps. The ECU uses 4-point interpolation as well and for a majority of the ECU's operation it is never reading just a single point in the maps. There is always "region" being used rather than a single independent cell value - the tracing we use for the ZEM shows the user these regions with no more or less usable accuracy than if the data was pulled via the OBD......... Basically: it works well. :)
