90dx

I have been working on a SR20 swap for a local with a 91 240SX and I was looking through his parts he received for it from the importer and I find his ecu.There is a dial externally accesible on the ecu that has some Japanese writing beside it Anybody know what this would be?The ECU came with his engine which is a blacktop from a 93 I beleive S13 in Japan.I would have taken a picture but I had no camera with me.I probably should go hit a 240SX forum but I know there is a few Nissan guys here.

surfer

its to switch between modes, normal running mode, diagnostics and something else i dont remember and i think it is also used to adjust the idle but am not sure.