According to EVE University, and I quote:

To calculate the locking time (in seconds):

So, in the following scenario, we have an Astero (attacker) and a Venture (the target), pretty simple. What we need to calculate the targeting time, is Astero’s scan resolution (620 mm) and Venture’s signature radius (40 m).

By doing the calculation above for this scenario, it results that the locking time would be 0.04 seconds, which is totally wrong.

I want to find out how to calculate correctly the targeting time.

Does anyone know how it really works?