First, there is no hatch rate contest listed for this hatchalong so don't know if official is warranted here.
Different people calculate hatch rate based on what they want to know.
Divide the number of chicks hatched by the number you set to get your most basic hatch rate.
You can divide the number of developed eggs that go into lockdown by the number of chicks that hatch to see a more defined hatch rate.
If you are doing a fertility check on a pen/flock. Divide the total number of eggs set by the number of clear (non-developing) eggs to tell you what percentage are fertile..and then the number of fertile eggs by the number that make to "lockdown" or hatch to get the hatch rate for the pen/flock.
Hope that is not TMI!