What is the correct keel length?
You will get a lot of different opinions on this, I like a keel that is 2’ to 2 1/4” on hens and 2 ¼ to 2 1/2” on cocks. It is hard to measure but I just us my index finger and my thumb. After you measure all the birds in you loft you will get a very good feel for it. The birds that spin the fastest you will find have the shorter keels. The bird must spin so fast you can't count tuns, it you can count turns the bird is poor.
Some people modify a ruler, they add a notch in it for a starting spot. Feel the keel with your fingers so you have a good ideal of the start and stop of the keel. Then measure it with the modified ruler that will somewhat hook on the start and use you thumb for the keel end. Keels have different shapes and lengths so it is not always an easy measurement.
The keel needs to have a cuve to it and that is part of what some people call the apple feel.
Short and Long keeled birds can spin fast. Breed what is best for you, breeding best to best and they will average out to be the shorter keeled birds. Help speed the process and breed best to best and body type.