# Air mass curve (dialog)

The “Air mass curve” dialog is used to display a curve of air mass coefficients and altitudes as a function of time. These values to useful in data post-processing to compute the extinction coefficients.

## Activating the dialog

The dialog can be activated:

- from the main menu: Plot ‣ Air mass.

The “Plot air mass” dialog appears. Fill in the object coordinates and the observer coordinates. Confirm the dialog.

## Air mass dialog

Air mass

(1) The actual data set is shown here.

(2) The list of available data sets is displayed here.

(3) You can switch the labels on the X axis between Julian date (JD) or date and time (UTC).

## Data sets

The following data sets are available:

- AIRMASS - The air mass coefficient

- ALTITUDE - The apparent altitude in degrees; positive values above the horizon, negative values below the horizon

## Context menu

You can select an individual point by a right click, you can also select more than one point by pressing a Shift key and left mouse button and drawing a rectangle in the graph. Then, click the right mouse button on a point in the selection to open the context menu. It provides following functions:

- Show frame - it shows a preview to a selected frame. It is not allowed when more than one frame is selected.

- Show properties - it opens a new dialog with properties of selected frame. It is not allowed when more than one frame is selected.

- Delete from data set - selected measurements are removed from the current curve, the data will be shown again when you make a new curve or Rebuild the actual curve.

- Remove from project - source frames corresponding to the selected measurements are removed permanently from the list of input files and such measurements won’t be included in any other output. It is not allowed to remove a reference frame.

## Statistics

The Statistics is a tool that computes and shows the minimum, maximum, sample mean and standard deviation.

To activate the tool:

1. From the local menu, select Tools ‣ Statistics. A new panel on the right side of the preview window appears.

If no points are selected, all points in the data set are included in the computation. To restrict the data for the statistics, press and hold the Shift key and draw a rectangle in a graph while you keep the left mouse button pressed down.

## Measurement

The Measurement tool displays two cursors in the graph. The cursors can be adjusted by dragging them using the left mouse button. The position of each cursor, their distance and statistics for the data between cursors is presented.

To activate the tool:

1. From the local menu, select Tools ‣ Measurement. A new panel on the right side of the preview window appears.

   Measurement tool

(1) Choose the axis you want to measure.

(2) Positions of the cursor 1 and 2 are displayed here.

(3) Distance between cursor 1 and 2.

(4) When cursors are defined on the independent (X) axis, number of points (frames) between cursor 1 and 2 are displayed and also minimum, maximum, mean value and sample deviation are presented.

See also

Light curve (dialog), Track curve (dialog), Object properties (dialog), CCD temperature (dialog)