..its not obvious at all. You wont nessecarily feel it at all and not notice it on the dyno. You will be more knocklimited than you have to and you are loosing out on power and reliability. When i first got aware of this 6-7 years ago i was trying to log RPM and other stuff for use with another third party software. Fair to say my logs were useless and it took me some thinking before i realized what was going on. Its usualy easiest to spot in a logfile where you view a rpm graph and especialy if you have rpm rate (rpm change pr second) shown in the graph also.. Severe cases can be seen on the tacho needle. Or with a timing light watching the mark during a pull. I could post a few graphs showing it again but i guess you all saw it before.