The GipsyX EOP file format supports an arbitrary length time series (monotonically increasing) of records.

A "#" anywhere in a line indicates that it and everything following it are comments and should be ignored by the reader.

An Info line describes the features of the immediate following data lines. There can be only one Info line per file.

An Info line must contain the following meta data:

Info: Number_fields: NN UT1TYPE: UT1 Extended_EO_Model: IERS10 EOEpoch: DD-MMM-YYYY HH:MM:SS.SSSS PreNut: IAU06 Data_Fixed_Interval: ddd

where

NN = number of fields in each data line (must be 10 or 18)
UT1 = type of UT1 data in the file (only UT1 is currently supported).
For UT1 type, tidal variations are removed internally before interpolation and added back afterward.
For a history of tidal models for the UT1 regularization, see further notes at the end of this file, which
explains some of the various types over the years.
IERS10 = name of the Earth_Orientation tides model.
Valid models are IERS10, IERS2020
IERS10 models include the HFEOP model recommended in the IERS2010 Conventions (TN36).
IERS2020 models include the HFEOP and libration models recommended in the IERS2020 Conventions.
EOEpoch = UTC epoch in character format for the rate models
IAU06 = name of the precession-nutation model.
Valid models are IAU80 and IAU06 (this is the precession/nutation model for IERS10 and IERS2020).
ddd = time interval in days between two data lines.

All key words contained in the Info line should be present, spelled and sorted in the order exactly as shown above.
The current list of key words is:
Number_fields
UT1TYPE
Extended_EO_Model
EOEpoch
PreNut
Data_Fixed_Interval

A data line contains 10 to 18 fields:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
UTC TAI-UTC TAI-UT1 (TAI-UT1)rate XP YP XPrate YPrate dPsi dEps UT1_sig UT1rate_sig XP_sig YP_sig XPrate_sig YPrate_sig Psi_sig Eps_sig
J2000sec sec sec sec/UTCsec arcsec arcsec/sec mas mas sec sec/sec arcsec arcsec/sec mas

where

1 UTC = epoch time of the data point in UTC second past J2000.0.
2 TAI-UTC = TAI - UTC in second (the leap seconds).
3 TAI-UT1 = TAI - UT1 in second.
4 (TAI-UT1)rate = rate of TAI-UT1 in second/UTC_second.
5 XP = X polar motion in arc second.
6 YP = Y polar motion in arc second.
7 XPrate = rate of XP in (arc second)/UTC_second.
8 YPrate = rate of YP in (arc second)/UTC_second.
9 dPsi = offset of nutation angle in longitude, in 1e-3 arc second.
10 dEps = offset of nutation angle in obliquity, in 1e-3 arc second.
fields 11 - 18 are optional, they are error range for date in fields 3 - 10.

Note on UT1 regularization:
Defined in IERS Conventions (2010) (IERS Techinical Note NO. 36) page 123:
"Past versions of the IERS Conventions defined regularized UT1 as UT1 with the
effect of the corrected tides with periods less than 35 days removed and UT1S as
UT1 with the effects of all tidal constituents removed, including the long-period
tides (up to 18.6 years)."

"UT1R was adopted at The Eighteenth General Assembly of the International Astronomical Union
to be UT1 with the short period tides removed, i.e., periods less than 35 days,
and that these tabulations be based on Yoder et al. (1981). See: Transactions of
the International Astronomical Union, 1983, Proceedings of the Eighteenth General Assembly,
Vol. XVIIIB, 17-26 August, 1982, Patras, Greece, pp. 238-240."
NOTE: UT1R is no longer supported in GEOP.

Internally, this Yoder et al (1981) model is referred to as 'OLD41T' model (41 terms).

When, the info line contains "UT1TYPE: UT1R", it is assumed that
the OLD41T model has been removed from the series and that model
will be used for UT1. There is no way to input a UT1R series with
the newer 62 term convention. Hermite interpolation of the input
UT1 series is always performed on the series after removal of the
tidal terms (either 41 or 62 terms).

Note on the dPsi and dEps fields:
The celestial pole offsets represent corrections in obliquity and in longitude to be applied
to the position of the celestial intermediate pole predicted by the precession and nutation
models. These corrections to the conventional models are determined by VLBI processing and
reported by the IERS in Bulletins A and B.
These corrections are only relevant when the IAU80 precession-nutation model is selected.
However, in GIPSY, even when the IAU80 model is used, the nutation parameters dPsi and dEps are
not actually computed based on the IAU 1980 Theory of Nutation. Indeed, for simplicity and to
speed up the computation, they are readily extracted from the planetary ephemerides. Therefore,
the corrections in obliquity and in longitude are not applied.
The corresponding fields in the GEOP file format were included for the sake of completeness; merely
as a way to record the information contained in Bulletins A and B.
NOTE: this is now historical information as there is no way to select IAU80 in GCORE.