OBS_NIST FILE (typically 'time.dat') This file contains clock offsets between observatory clocks (to which TOAs are referenced) and UTC(NIST). This file may either have fixed format or flexible format. In fixed format, each line has the following format: col item 1-9 MJD 10-21 offset1 (us) 22-33 offset2 (us) 35-35 observatory code 37-37 flag The difference offset1-offset2 is ObservatoryTime-UTC(NIST). If the flag is ' ' (blank), offsets from the two entries closest to the target MJD are linearly interpolated. If the flag is 'f', the closest entry to the target MJD is used without interpolation. In flexible format, each line has the following format: OFFSET [fixed] The first six columns must be 'OFFSET' (case insensitive). The site may be a 1- or 2-character observatory code. MJD and offset play the role of MJD and offset2 in the fixed-format headers described above; the optional word "fixed" plays the role of the 'f' flag described above. In either format, lines that begin with "#" or "MJD" or "=====" are ignored, Lines of the form "INCLUDE " may be used at any point to incorporate additional. files. Clock offsets from a given observatory must be in chronological order, but offsets from different observatories may be intermixed. NIST_UTC, NIST_BIPM, NIST_PTB, NIST_AT1 FILES These files contain clock offsets between UTC(NIST) and other timescales. The first two lines of these file are ignored. Subsequent lines have the format: col item 1-10 MJD 11-29 offset The offset is xxx-UTC(NIST) in nanoseconds, where xxx is UTC, TT(BIPM), UTC(PTB), or AT1. Linear interpolation between entries is performed. UT1 FILE (typically 'ut1.dat') This file contains values of UT1-UTC, TAI-UT1, or A1-UT1 (indicated by setting the KIND variable in the header to 1, 2, or 3, respectively). The first line of this file is ignored. Line 2 has the following format: col item 1-32 VARFMT, the format of data lines in Fortran notation 33-34 KIND 36-42 start JD (integer) 44-50 end JD (integer, set to a high value to read to end of file) 52-54 the number of entries per data line 56-58 interval, in days, between each entry on a data line 60-74 UNITS (e.g., 1E-3 means milliseconds) Subsequent lines contain a control string, MJD, and offset entries in the format described by the VARFMT variable. If the control string reads 'END', any further lines of the file are ignored. LEAP SECOND FILE File 'leap.sec' in the clkdir directory contains a list of leap seconds. One date is stored per line, in ascending order. Dates are MJDs.