The use of two computer words to represent each number. This technique allows the use of twice as many digits as are normally available and is used when extra precision is needed in calculations.
An IEEE floating-point format in which a value occupies 64 bits: 1 bit for the sign, 11 bits for the exponent, and 52 bits for the fraction. See also single-precision, quad-precision.
Refers to a level of coordinate accuracy based on the possible number of significant digits that can be stored for each coordinate. Whereas single-precision coverages can store up to 7 significant digits for each coordinate and thus retain a precision of 1 metre in an extent of 1,000,000 metres, double precision coverages can store up to 15 significant digits per coordinate (typically 13-14 significant digits) and therefore retain the accuracy of much less than 1 metre at a global extent.