Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

I switched out my regular SunDec hour meter which was on my Toro 828 LXE for the tach/hour meter version that I was going to use on a 17 hp lawn tractor this spring.  I did this out of curiosity to make sure my engine is running at its rated speed, whatever that is.  At idle, my 8hp L-head engine runs at about 2,300 RPM and at full operating speed, read at about 3,350 Rpm's.  I'm not so concerned about the idle, rather if the operating RPM is correct.  Does anyone know what percentage of error these meters are rated at that simply tap off the spark plug wire?  I want to make sure the engine is producing the correct amount of power.  Thanks.