Hi, It was bought because it is used on our old 440,460 and 660 saws as we have being experiencing "bad fuel" probs over the last 15 months/2 years 's or so. We bought the 280i's because of this and had no probs at all. The big saws were getting worse and we thought this was wear and tear. Because of this and issuses with our old FS450 brush-cutters, we bought 1 441cm and no probs! so on that saw over 5 or so days, we upped the bar from 20" to 25"- did 5 consectutive cuts,stopped it, restart and different saw! so we did the same with 30" bar and same! Awsome power but big difference in fuel ie uses more - alot! Because of this I bought 7 more and they all run perfect. The tacho is used to tune the old 441 carb saws max revs on the big bars ie 30" etc. It is an acoustic one so you can set the paramiters to how you want to - so stopping over reving with the fueling etc. Fuel and emmissions are a major headache and so is wrecked saws so it serves a purpose for the older saws that are having to run on awful petrol! It works as we have found 6 out of 5 saws-the rev limiter was 900 -1500 rpm out!! ie under reving!