Being able to do this quickly can be a really useful skill - it lets you figure out roughly what someone's fit might be before you actually engage them, and can help you decide the best way to proceed in a fight. Recognising the difference between blasters and railguns, or medium and small guns on a cruiser, is likely to have a significant difference on the range you want to engage at or even whether you want to take the fight at all. Even different calibre guns within the same class can give you an idea of what other modules your opponent might be fitting (for example a rupture with 425mm autocannons will generally be shield fit, while dual 180mm autocannons suggests a heavy armour tank).
The original chart didn't include capital weapons, and I've since had a few requests to add them in. There have also been a couple of name changes which made the old chart potentially misleading, so I figured it was time for an update!
Have a browse through the chart, and then try looking at a few ships in space and see if you can figure out what they're fitting!
As before, I've also produced a high-res version suitable for printing.