The JPI engine instrument is a great tool to not only assist in the proper leaning of the engines but to also monitor the health of the engines ... there are numerous articles written where pilots have seen a change in the engine monitor long (hours/flights) before there would have been any other indication of a potential problem ... you can download the flights and maintain a history of each cylinder; how its performing, if there are any changes, etc ... JPI is not just a tool -- it is a piece of safety equipment -- know what your engines are doing !!!