A laborer or labourer — see variation in English spelling — is a person who does one of the construction trades, traditionally considered unskilled manual labor, as opposed to skilled labor.[clarification needed] In the division of labor, laborers have all blasting, hand tools, power tools, air tools, and small heavy equipment, and act as assistants to other trades, e.g., operators or cement masons. The 1st century BC engineer Vitruvius writes in detail about laborer practices at that time. In his experience a good crew of laborers is just as valuable as any other aspect of construction. Other than the addition of pneumatics, laborer practices have changed little. With the advent of advanced technology and its introduction into the construction field, the laborers have been quick to include much of this technology as being laborers work.