Yep, narrow band. I have used one of these gauges in the past and they're not very effective. The narrow band sensor switches very rapidly between reading rich and reading lean, it also has a relatively slow response time and is quite temperature sensitive. For WOT and idle it is no good, it can be quite good for tuning off load once you get the hang of how it works. If you can hook it up to a datalogger then it is much more effective. The money would be better spent on a dyno session, otherwise the plug colour and a stopwatch is hard to beat.
