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.
1 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). 2  High end architectural shingles, however, could run as much as $6 to $8 per square foot installed ($9,000 to $12,000).