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ObsReduce is an MS Windows program that reduces observations of satellites relative to the backgroun

This capability is required when reducing observations of objects for which orbital elements do not exist, or are very inaccurate. As long as the coordinates in the immediate vicinity of the reference stars are known, they can be displayed in the FOV, and the observation reduced.
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It is important to note that the FOV centre date/time is distinct from the observation date/time, even though they usually have the same value. Keeping them distinct enables the object to be moved back and forth along its predicted track, which necessarily changes the prediction time, while preserving the observation date/time.
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By design, whenever the observation date/time is entered or edited, the FOV Centre date/time  is automatically synchronized to match, on the assumption that the predicted track will be sufficiently accurate to place the reference stars near the centre of the FOV at the time they were observed.
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R.A. and Dec or AZimuth and ELevation entries take effect when the mouse cursor leaves the text box, such as when the Enter key is pressed, or the mouse is physically moved out of the box.
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<B><a name="Move">D.15 &nbsp;Move Satellite Frame</B>
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The controls in the Move Satellite frame enable an object to be moved backward or forward along its predicted track.
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There are two sets of increment/decrement buttons: one that moves the satellite in increments that are some percentage of the diameter of the FOV; the other in increments of time in seconds. The size of either increment may be changed at run-time.
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Both methods ultimately involve changing the time. When moving in increments of FOV diameter, the time increment is computed internally by dividing the angular increment by the object's angular velocity.
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I believe that most users will prefer to move objects in increments of the FOV diameter, because angular velocity is automatically taken into account, ensuring that the object moves  in constant, predictable steps, everywhere along its track.
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A powerful feature is the ability to specify the element of time to be incremented, selected using the "by changing" option buttons: FOV Time or Early/Late.
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If the time difference between the observation and prediction is small, or if it is large, but its size known and entered in the <a href="#Early/Late">Satellite Early / Late</a> text box, then incrementing the FOV Time (i.e. the date/time in the FOV Centre frame) will produce accurate plots.
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If the satellite is significantly early or late by an unknown interval, and the location of the reference stars is unknown, but you have a good sketch of them and a few surrounding stars in the field of view, then follow the steps in <a href="#C.1.3">Section C.1.3</a> to use Move Satellite to help bring them into the FOV.
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<B><a name="Autoclear">D.15.1 &nbsp;Automatic Observation Clearing</B>
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Whenever you enter an object's <a href="#Geometry">geometrical and positional</a> data, ObsReduce remembers the coordinates of the centre of the field of view. If a subsequent Move Satellite command causes those coordinates to move out of the field of view, then ObsReduce clears the positional entries and resets the time and position accuracy to their default values.
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Similarly, causing stars that have been selected to exit the field of view, causes them to be automatically de-selected, clears the results of any reduction, clears the positional entries, and resets the time and position accuracy to their default values.
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<B><a name="FOVsettings">D.16 &nbsp;FOV Settings Frame</B>
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The controls in the FOV Settings frame enable the user to change the diameter, limiting magnitude and orientation of the field of view.
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The FOV diameter may be varied between 0.1 deg and 20 deg. The default value may be set at line 26 of the ObsReduce.ini file. The limiting magnitude may be set no brighter than 5. The default value may be set at line 28 of the ObsReduce.ini file.
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The orientation may be set to erect, inverted or mirror image, using the option buttons. It is important to note that the program interprets star selection, geometry and position entries consistent with the orientation. If the orientation is changed after a reduction has been made, the program automatically changes orientation and position entries to agree with the new orientation, such that the reduced observation does not change. The default orientation may be set at line 27 of the ObsReduce.ini file.
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<B><a name="Result">D.17 &nbsp;Result Box</B>
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The IOD, UK, or RDE formatted result is displayed in the long text box near the bottom of the display.
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<B><a name="Save">D.18 &nbsp;Save Button</B>
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Before saving your results, you should review your inputs to make certain they are correct. You may change any input and the result will be immediately reflected in the formatted observation at the bottom of the window.
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For R.A. and Dec, ObsReduce enables you to change the number of significant digits after the decimal point from their default values, by using the increment/decrement buttons at the bottom of the window. UK format users can do likewise for the positional accuracy. To change your default values, edit lines 15 - 17 of ObsReduce.ini.
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When you are satisfied with the accuracy and format of your results, you may save them by hitting the Save button.
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<B><a name="Obsfiles">D.18.1 &nbsp;Observation Files</B>
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As shipped, ObsReduce creates a directory named Observations as a subdirectory of the one in which it was installed. All four types of output file will be written to that sub-directory.
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Results.obs is a text file log of all of your observations, in the chosen format.
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For RDE (Russell Eberst) format, ObsReduce automatically writes the start-of-month header line, as well as the day of the month lines. It automatically keeps track of the need for such entries in a file called lastsessiondate.txt.
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Details.obs is a text file log of the underlying details of your observations: coordinates and magnitude of reference stars, geometry, miss distance, as in this example:
<PRE>
2003 Jul 15  03:21:44.23 UTC   96072A    24680

(Base: 2003 Jul 14  23:36:23.42 UTC + 03:45:20.81 elapsed. Drift = 0.0 s/h)

Star A: 14:30:30.5348  -04:03:54.715  (2000.0) Mag 7.41
Star B: 14:30:00.1397  -04:14:49.960  (2000.0) Mag 7.04

Object on line AB, 0.300 from A to B;  Star Sep = 0.222 deg

Object: 14:30:21.4050  -04:07:11.331  (2000.0)  +/- 0.011 deg (0.050 X Star Sep)

Obs - Pred: 0.036 deg X-track; 0.142 s early, relative 1.22 day old elset:

1 24680U 96072A   03194.91931763  .00014500  00000-0  15976-3 0    04
2 24680  97.8240 257.5084 0499000 278.3339  81.6660 14.82681039    09

24680 96 072A   2701 G 20030715032144230 17 25 1430357-040719 77 S
</PRE>
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Session logs of the same information are stored in files named yyyymmdd.obs and yyyymmdd.det.
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ObsReduce can only append to those files, so there is no danger that it will overwrite your data. Of course, it is prudent to make periodic backups.
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You can change the location of the files, or cause some of them not to be produced, by editing lines 29 through 32 of ObsReduce.ini.

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<B><a name="Sep">D.19 &nbsp;Star Sep Box</B>
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The star sep is the angular separation between the reference stars used in a reduction. It is displayed automatically each time a reduction is computed.
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<B><a name="Standard">D.20 &nbsp;Std. Pos Accy Box</B>
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The standard positional accuracy is computed automatically each time a reduction is computed, as described in <a href="#PosAccy">Section D.9.1.4</a>.
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<B><a name="SigDec">D.21 &nbsp;Significant Decimals Buttons</B>
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The number of significant positions after the decimal of IOD and UK formatted results can be changed via the increment/decrement buttons located at the bottom of the window. Default values may be set by editing lines 15 and 16 of the ObsReduce.ini file. The program enforces the maximum and minimum number of significant positions as defined for each format.
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UK format users may also vary the number of significant digits of the positional accuracy, using the increment/decrement button located at the bottom, right of the window. The default value may be set by editing line 17 of the ObsReduce.ini file.
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<B><a name="Clear">D.22 &nbsp;Clear Position Button</B>
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The Clear Position button clears the entries made in the Position frame, the results of the reduction, all star selections, and resets the time and position accuracy to their default values. All else remains the same.
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The same level of clearing occurs after a result has been saved.
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<B><a name="Addstars">D.23 &nbsp;Adding Stars to the Database</B>
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Although, ObsReduce's star database is derived from the Tycho 2 catalogue, which contains millions of stars, it is not complete, especially, but not exclusively, at the faintest magnitudes. As a result, you may occasionally find that a reference star you are certain exists, is not displayed by ObsReduce. Also, planets and asteroids appear star-like, and may occasionally be used as reference stars, but are not displayed by ObsReduce.
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To mitigate such problems, ObsReduce supports the addition of stars to its database.
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To add stars to the data base, create a text file named addstars.txt, and place it in the same folder (directory) that contains ObsReduce's star data files.
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The data for each star added to the file must reside on one line, consisting of the following values:
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1. Right ascension, 2000.0, radians<br>
2. Proper motion of right ascension, mas/yr (i.e milli arc seconds per year)<br>
3. Declination, 2000.0, radians<br>
4. Proper motion of declination,(i.e milli arc seconds per year)<br>
5. Visual magnitude<br>
6. Comment or description (optional)
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These values must appear in the above order, on a single line, separated by one or more spaces. If you do not know a star's proper motion, or the object is non-stellar, e.g. a planet or asteroid, enter proper motion as 0, for example:
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0.6569371308 &nbsp; 0 &nbsp; +1.55789494993 &nbsp; 0 &nbsp; 8.20&nbsp; &nbsp;star
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Since non-stellar objects change position rapidly, it is recommended to remove them upon completion of the reduction in which they were used. Alternatively, they may be prevented from being displayed by inserting a semi-colon at the start of the line, for example:
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;3.3033984925 &nbsp; 0 &nbsp; +0.06893177881 &nbsp; 0 &nbsp; 7.26&nbsp; &nbsp;Pallas on 2005 Mar 09 at 10:51 UTC
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Addstars.txt is read each time the simulated FOV is updated, so it is not necessary to restart ObsReduce for changes to the file to take effect.
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<H3><a name="Acknowledgements">E. &nbsp;Acknowledgements</H3>
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Thank you David Brierley, Mike McCants, Ken Smith and Allen Thomson, for your encouragement, technical advice and alpha testing during the early development of ObsReduce.
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Special thanks to Scott Campbell, who developed the algorithms used to reduce observations made with cameras, and performed the first beta tests of them.
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<H3><a name="Install">F. &nbsp;Installation</H3>
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<B>Disclaimer: You install and use ObsReduce at your own risk. Ted Molcza