Reading the chrono: FPS, joules and shot strings
How FPS becomes joules, why one shot is not enough, and which number the field looks at.
FPS or joules
FPS depends on the BB weight, while joules show the real energy, which is why most fields write their limits in joules. The formula is half the mass times the speed squared: 350 FPS with 0.20g is 1.14J.
Why one shot is not enough
Chrono a string of several shots with the BBs you play with and the hop-up set for play. The rules of several fields ask for exactly that.
Look at the hottest shot, not the average: the calculator assesses a string by it, because that is the number that can put you over the limit. A wide spread between shots points to the air seal, the hop rubber or BB quality.
How much margin to leave
Two chronographs rarely read the same. The calculator marks anything within 5% of the limit as borderline. If you are there, turn the power down before you reach the chrono table.
On gas replicas temperature moves the result, so chrono in similar conditions or check the prediction in the gas and temperature panel.