Frequency and hertz
Hertz is a generic unit of frequency that tells us how often something will happen. in this case it lets us know how many times the flash will fire in one second. so at 1Hz it fires once per second, at 10Hz 10 flashes per second. Many flashes will also have a flash count setting that lets us determine the total number of flashes. We can divide the flash count by the hertz to come up with the correct shutter speed for our flashes. for example, if the flash count is 10 and the Hertz is 20, we know we’ll get 10 flashes in half a second.