Technology is represented as n-m level. n is the primary tech level. m is the technology's sublevel. The following information should help you understand:
For each of these technologies there are 5 levels of improvement. Each level is considered a technology sublevel. Therefore, the 3rd improvement of a Cannon is 1-3 and the 4th improvement of a Flak is 2-4.
All stats on this site are listed at x-3 sublevel. To compute the specs for other sublevels use the following table:
Note that only those rows in "bold" in your ingame technology panel change with sublevel changes.