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Help with the Cursor Box

======================== The Cursor is a box that can be adjusted from 3x3 to 31x31. In the center of the box is a '+' and the corners of the box are displayed in sizes 7x7 and larger. You can increase the size of the box by holding down the {Ctrl} key and pressing { -> }. You can decrease the size of the box by holding down the {Ctrl} key and pressing { <- }. The size will roll over, i.e., increasing the size from 31x31 produces 3x3 and decreasing the size from 3x3 will produce 31x31.

The size of the box plays a key role in many measurements. The average value and noise number displayed at the top of the Examine Image screen gives the average pixel value in the box and the noise is the RMS deviation from that average. When you set the background threshold with the T key, the average value at that point is stored for future use.

The magnitude measurement depends upon the background threshold, as this value is subtracted from the measurement of a star field to isolate the star's contribution. Likewise, the 'Point' or 'Position' (P key) function subtracts the background to isolate the star's contribution for calculating the center of the stellar image.