Hi gazzastrip - and welcome... The truth is that activity in the airlock does not tell you anything useful. Bubbles can be caused by a change in air pressure in the atmosphere in a liquid saturated with CO2 now forced to escape. A lack of bubbles can point to tiny leaks between the airlock and the bung or bung and vessel... The only reliable method of knowing when a fermentation has ceased is with an hydrometer. You are (as you know) looking for changes in density - otherwise known as "specific gravity". No change over three measurements over a week or two tells you that there is no more fermentation on going... whether that itself means that there is no more sugar left for the yeast to ferment will depend on the actual reading, but fermentation can stop for a variety of reasons even when there is a great deal of sugar remaining. You need an hydrometer. Counting bubbles might be fun... but it's not reliable and not useful. (in fact many seasoned wine makers only use an airlock in the secondary and loosely cover their primary fermenter with a clean cloth... No airlock, no bubbles... ).