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.
Depending on budget constraints and the shape and slope of roof that needs to be worked on, options vary. One type of roofing material commonly used is roll roofing. Roll roofing works like traditional shingle-clad roofing to protect the underlayment of the roof's structure. There are many reasons why contractors choose roll roofing.