This value is the amount of ignition retard applied to each cylinder due to knock. Lower quality fuels are more susceptible to detonation. Knock become more worrisome as engine load increases. Occasional knock counts are bound to happen at low load, shifts, and high throttle transients. However if you are noticing that you are consistently seeing knock counts greater than -5* in multiple cylinders you may consider switching gas stations or trying a higher octane fuel for a tank or two.