North London line then it was switched to . Later, it was cut back to . A tunnel, the Hampstead Heath tunnel, runs under Hampstead between and . The line is double track throughout, with a mix of triple and quadruple track between and . The former North Woolwich branch included a section of single track between Custom House and North Woolwich stations, and the Broad Street branch was at one time formed of quadruple track. During the February–May 2010 blockade, the , and stations were rebuilt to allow the extended East London line to serve Highbury & Islington on fully segregated tracks
Quadruple-precision floating-point format implement nearly quadruple precision using "pairs" of double-precision values is sometimes called double-double arithmetic. Using pairs of IEEE double-precision values with 53-bit significands, double-double arithmetic can represent operations with at least a 2×53=106-bit significand (actually 107 bits except for some of the largest values, due to the limited exponent range), only slightly less precise than the 113-bit significand of IEEE binary128 quadruple precision. The range of a double-double remains essentially the same as the double-precision format because the exponent has still 11 bits, significantly lower than the 15-bit exponent of IEEE quadruple precision (a range of for double-double versus for