Derived measures
air changes per hour (ACH), a measure of the replacements of air within a defined space used for indoor air quality
ampere hour (Ah), a measure of electrical charge used in electrochemistry
BTU-hour, a measure of power used in the power industry and for air conditioners and heaters
credit hour, a measure of an academic courses contracted instructional time per week for a semester
horsepower-hour (hph), a measure of energy used in the railroad industry
hour angle, a measure of the angle between the meridian plane and the hour circle passing through a certain point used in the equatorial coordinate system
kilometres per hour (km/h), a measure of land speed
kilowatt-hour (kWh), a measure of energy commonly used as an electrical billing unit
knot (kn), a measure of nautical miles per hour, used for maritime and aerial speed
man-hour, the amount of work performed by the average worker in one hour, used in productivity analysis
metre per hour (m/h), a measure of slow speeds
mile per hour (mph), a measure of land speed
passengers per hour per direction (p/h/d), a measure of the capacity of public transportation systems
pound per hour (PPH), a measure of mass flow used for engines fuel flow
work or working hour, a measure of working time used in various regulations, such as those distinguishing part- and full-time employment and those limiting truck drivers working hours or hours of service

See also
Liturgy of the Hours
Horology
Horae, the deified hours of ancient Greece and Rome
Hexadecimal hour, a proposed unit lasting 1 h 30 min
Decimal hour or deciday, a French Revolutionary unit lasting 2 h 24 min
Golden Hour & Blue Hour in photography
Metric time

Notes
References
Bibliography
Further reading
Gerhard Dohrn-van Rossum (1996).
Two fire-spitting cobras were said to guard the gates of each hour of the underworld, and Wadjet and the rearing cobra (uraeus) were also sometimes referenced as wnwt from their role protecting the dead through these gates. The Egyptian word for astronomer, used as a synonym for priest, was wnwty, "one of the wnwt", as it were "one of the hours". The earliest forms of wnwt include one or three stars, with the later solar hours including the determinative hieroglyph for "sun". East Asia
Ancient China divided its day into 100 "marks" (Chinese: 刻, oc *kʰək, p kè) running from midnight to midnight. The system is said to have been used since remote antiquity, credited to the legendary Yellow Emperor, but is first attested in Han-era water clocks and in the 2nd-century history of that dynasty. It was measured with sundials and water clocks. Into the Eastern Han, the Chinese measured their day schematically, adding the 20-ke difference between the solstices evenly throughout the year, one every nine days. During the night, time was more commonly reckoned during the night by the "watches" (Chinese: 更, oc *kæŋ, p gēng) of the guard, which were reckoned as a fifth of the time from sunset to sunrise.Imperial China continued to use ke and geng but also began to divide the day into 12 "double hours" (t 時, s 时, oc *də, p shí, lit. "time[s]") named after the earthly branches and sometimes also known by the name of the corresponding animal of the Chinese zodiac.