The SI unit for period is the second. For counts per unit of time, the SI unit for frequency is hertz (Hz), named after the German physicist Heinrich Hertz; 1 Hz means that an event repeats once per second.A previous name for this unit was cycles per second (cps).or each dot, f is the frequency in hertz (Hz) â meaning the number of times per second (i.e. cycles per second) that it flashes â while T is the flashes' period in seconds (s), meaning the number of seconds per cycle. Each T and f are reciprocal.
Photo: CertainTeed. Economical to produce, relatively easy to install and widely available, asphalt shingles are todayâs most popular roofing materialânot only because theyâre less costly than wood, wood shakes, tile, metal or slate, but also because their guaranteed life span pits them favorably against competitors.
In Australia this type of carpenter is called a roof carpenter and the term roofer refers to someone who installs the roof cladding (tiles, tin, etc.).In the United States, the most common roofing material is asphalt shingles. German roofer installing a reed roof (he is wearing the traditional vest and trousers of a crafts person). Roofers laying a tiled roof in Denver, Colorado. A roofer or roof mechanic is a construction worker who specializes in roof construction.