Their purpose is to implement Boolean Logic. You might notice the correspondence to Binary Semantics and thus Binary (number system) logic & mathematics. Special fun: OR and XOR (exclusive OR).
Geographical Considerations: While most contractors will price their asphalt shingles roof replacement services within $4.00 to to $7.00 per square foot or $400 to $700 per square range, there will be significant geographic variations.
Asphalt Shingle Roof Average Costs. The actual cost of an asphalt shingle roof may vary depending on the materials used, your location, the complexity of the installation (i.e. roof slope and home height), and other factors. 3-Tab asphalt shingles cost $1.50 to $3.50 per square foot. For an average-sized (1,500 square foot roof), the total cost might be $2,250 to $5,250. Architectural asphalt roof shingles cost, on average, cost around 20 to 40 percent more than 3-Tab shingles, or $2.50 to $5.00 per square foot installed ($3,750 to $7,500). High end architectural shingles, however, could run as much as $6 to $8 per square foot installed ($9,000 to $12,000).