Tropical cyclone scales barometric pressure is low compared with its surroundings. Other classifications historically used include: cyclonic storm where the winds did not exceed force 10 on the Beaufort scale and a Cyclone where the winds are either force 11 and 12 on the Beaufort scale. Between 1924 and 1988, tropical cyclones were classified into four categories: depression, deep depression, cyclonic storms and severe cyclonic storms. However, a change was made during 1988 to introduce the category "severe cyclonic storm with core of hurricane winds" for tropical cyclones, with wind speeds of more than . During 1999 the categories Very Severe Cyclonic Storm
Fujita scale F1 corresponds to the twelfth level of the Beaufort scale, and F12 corresponds to Mach number 1.0. F0 was placed at a position specifying no damage (approximately the eighth level of the Beaufort scale), in analogy to how the Beaufort's zeroth level specifies little to no wind. From these wind speed numbers, qualitative descriptions of damage were made for each category of the Fujita scale, and then these descriptions were used to classify tornadoes. The diagram on the right illustrates the relationship between the Beaufort, Fujita, and Mach number scales. At the time Fujita derived the scale, little information was