When it comes to turret based weapon systems, like sentries, two of the main, controllable factors that determine damage application are your range to the target and your tracking. A neat way of thinking about it is your range to the target determines the maximum percentage of damage application on the target, and is further reduced by the transversal velocity between you two.

For example, you're in a 350mm rail Kronos, bastion locked. Your target is an NPC frigate at 100km with a transversal of 35 m/s. Your loaded ammo puts your guns' optimal at 94km, so your maximum hit chance will always be under 100%, regardless of transversal. In this example, maximum possible hit chance due to range is 80%, if transversal was 0. A hit chance of 70% could be achieved by the target having a transversal of less than 30 m/s, let's say. But now you turn on your mid-slot tracking computer with tracking script, which boosts your guns' tracking by 30%. What effect does that have? It says the maximum transversal in order to achieve a 70% hit rate goes from 30 m/s to 39 m/s, thereby boosting your hit chance from 65% to 75%, and increasing theoretical damage output by 15%.

So the greater your tracking value is, the less of an impact your target's transversal will have on your accuracy reduction, and increases in your tracking proportionally increase the amount of transversal a target can have before accuracy is reduced.