Settings area
Control window Settings area
Note: Some controls are marked with a * if their current values can be saved as the default value using the 
Save as new defaults button.
Values for Start and End image number must be entered manually unless FITS files are dropped into the FITS files area.
If entering manually, images are assumed to be equally spaced in time. Enter a sequential number for the first and last image used.
Start and End can range from 1 to 9999. The Start number can be greater than 1. The End number must be greater than the Start number. The current End number can be saved as the default value using the Save as new defaults button.
Start and End times are optional, but if present will be used to calculate the time relating to the mouse position on the Screen Ruler window. See Displaying coordinates via the mouse. Values for Start and End time must be entered manually unless FITS files are dropped into the FITS files area.
If entering times manually, enter a time for the first and last image used. The times are entered as 24 h values in hhmmss (hours, minutes, seconds) format or in hh:mm:ss format. If the Start time is after the End time then it is assumed that midnight has been crossed and the End time is in the day following the Start day. Enter a convenient but consistent time used in your images, e.g. use the exposure start time for both Start and End times, or the exposure mid-time for both Start and End times.
Swaps the start and end coordinates of the Screen Ruler line, reversing the direction of the Screen Ruler arrow if displayed. The Start and End numbers and the Start and End times if present are left unchanged.
Tick the Show arrow? control to display an arrowhead at the end point of the Screen Ruler line. Use the Arrow Size control to increase or decrease the arrowhead size, between 5 - 20 pixels.
Change the width of the Screen Ruler line, between 1 - 6 pixels. Click on the coloured square to choose a colour for the Screen Ruler line. The current settings for both controls can be saved as default values using the Save as new defaults button.
Note that the thin dotted extension line on either end of the Screen Ruler is always displayed and is not adjustable.
Opacity % controls the semi-transparency of the Screen Ruler, in the range 5 % (almost invisible) to 100 % (completely opaque). When the Screen Ruler window has focus and the Alt key is pressed the Opacity is temporarily changed to 1%, effectively hiding the ruler. Click on the coloured square to choose a background colour for the Screen Ruler window. The current settings for both controls can be saved as default values using the Save as new defaults button.
The position angle in degrees (P.A.°) of the Screen Ruler line is displayed in the status area of the Screen Ruler window:
P.A.° uses the convention North = 0°, East = 90°, South = 180°, West = 270°, i.e.:
Astronomical images may not be aligned so that North is exactly "up" and therefore the value of the P.A.° on the Screen Ruler may be in error. Use this control to correct for the rotation in the underlying images if the Ruler is being used to measure position angles in images. The value required is the value of "Rotation" in the Astrometrica log after an image is solved which is also the value of the negated FITS keyword CROTA2 i.e. (-1 * CROTA2) if present in the FITS file. Image rotation° is automatically set if FITS files dropped into the FITS files area contain the FITS keyword CROTA1 or CROTA2. The rotation value value is taken from the first of the dropped FITS files that contain a valid value.
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