Missed in my other response: Double gives about double the precision, not 4 times, that of a single: "The 53-bit significand precision gives from 15 to 17 sign

Missed in my other response: Double gives about double the precision, not 4 times, that of a single: "The 53-bit significand precision gives from 15 to 17 significant decimal digits precision (2−53 ≈ 1.11 × 10−16). If a decimal string with at most 15 significant digits is converted to the IEEE 754 double-precision format, giving a normal number, and then converted back to a decimal string with the same number of digits" (from Wikipedia)