Re: chrony alpha master chronograph
If the figure you got was higher than expected, make sure you have opened the Chrony completely; if it's not perfectly flat the sensors will be closer together and the velocity will be higher.
If the figure you got was slower than expected, make sure you are shooting across the sensors in a very straight line, no up or down or left to right ot right to left; it has to be the shortest route possible. It is also not impossible that books inflate their velocity a little.