ResidualsAstrometric observation residuals are the difference between an observed and a calculated position (this is known as an O-C residual).
The residuals listed in the MPES are of two kinds: optical and radar.
The optical residuals are given for observations made visually, photographically or with a CCD. The date of observation (YYYYMMDD form) is given first, followed by the observatory code where the observation was made, and then the r.m.s. residuals in R.A. and Decl. (both in arc-seconds, the R.A. residual including the cos(decl) term). If an observation was rejected from the solution, the R.A. and Decl. residuals are enclosed in parentheses. Following the R.A. and Decl. residuals, there may be an "X" (indicating an approximate position) or a "Y" (indicating a semi-accurate position).
The radar residuals are given for radar observations. The date of observation (YYYYMMDD form) is given first, followed by the observatory code of the tranmission site and the observatory code of the reception site. Then comes a "D" if the radar observation is a Doppler observation, "R" if it is a range observation. Then the residual (in s.d. of the observer-specified uncertainty in the measurement) is given. If the observation has been rejected from the orbit solution, the "D" or "R" is replaced by "d" or "r".
Note that residual blocks for unperturbed orbit solutions do not indicate which observations were rejected from the orbit solution. They simply show how the observations are represented with respect to the orbit solution.
The copying of residuals blocks for use in the Web is a low-priority task that is generally not run until several hours after the DOU MPEC is prepared. Also note that updated residual blocks may become available in the MPES before the orbits appear on DOU MPECs.
Note that in displayed residual blocks the code 413, 675 and 809 are used to represent observations from all observatory codes associated with that site. E.g., codes 262 and I03 are ESO and both are displayed as 809.