Depending on the bow and draw length and weight speed can be as little or nothing and as much as 12 fps.
I went around and measured all my large single cams and dual cam bows. The first speed nock is right at 4 1/8" from the bottom axle. Additional nocks go up the string. Most have 2 speed nocks (brass string nocks) and covered with shrink tubes. One single cam bow has 3 speed nocks as a 4th and 5th didn't make a difference and began to tetter on giving a slightly slower speed. My wheel bows and a Command Cam bow do not have speed nocks as they proved useless - these cams are small.
When trying speed nocks it's a trial and error thing. When chronographing have it set where it won't be moved until done and make a mark on the floor for foot placement - same distance from chronograph each and every time. Understand, the arrow begins losing speed as soon as it leaves the string. Normal distance from the face of a chronograph is given as one arrow length from the tip of the arrow or that the arrow is clear of the bow before crossing the first sensor.
My chrono os an app on my phone, dont own one but this is pretty accurate