By rapidly clicking the hook for a variable number of times at roughly 5 to 10 clicks per second, separated by intervals of roughly one second, the caller can dial numbers as if they were using the rotary dial. The pulse counter in the exchange counts the pulses or clicks and interprets them in two possible ways. Depending on continent and country, one click with a following interval can be either "one" or "zero" and subsequent clicks before the interval are additively counted. This renders ten consecutive clicks being either "zero" or "nine", respectively. Some exchanges allow using additional clicks for special controls, but numbers 0-9 now fall in one of these two standards. One special code, "flash", is a very short single click, possible but hard to simulate. Back in the day of rotary dial, technically identical phone sets were marketed in multiple areas of the world, only with plugs matched by country and the dials being bezeled with the local standard numbers.