The Number of Measurements is controlled at upper right. New measurement positions are added to the end of the list and are evenly spaced. To get all the measurements evenly spaced, first change the number of measurements to 1, tab out of the edit field (or click elsewhere in the window) and then change the number of measurements to the desired value.
The Add to Calculated field is available to adjust for baseline differences between observations and calculated values. This can be set manually or by pressing the Use Mean Offset button, which will insert the mean offset between observed and calculated values into this field. This is often essential with total field strength measurements.
The component of the magnetic field being fit can be changed using the popup menu at the left near the window's top. Choices are the total magnetic field, its horizontal component, and its vertical component.
The spreadsheet of values comprises most of the window. Listed are the horizontal (X) and vertical (Z) positions of the measurement points, the observed value, its uncertainty (if that option is chosen in the Preferences Window), and the calculated value. Clicking on this area and then clicking on the value to be changed will allow you to edit that value. Tabs will move you forward through the list; shift-tab will move backwards. Arrow keys allow movement up and down, right and left. Values and the Section Window are changed when the cell being edited becomes inactive (by selecting another cell or another window). Clicking on the header at the top of a column will sort the fits by values in that column. Column widths can be resized by clicking on the dividers between headers.
The RMS Misfit at the top of the window is the root mean square of the differences between observed and calculated values and is updated when calculated or observed values are changed.
You can read in data in a simple text file using the Import Delimited Text... command in the File menu. Files can have header lines that will be ignored (Lines to skip) and the X, Z, and observed magnetic values (total field, vertical component, horizontal component) can be in any columns. X and Z values and at least one of the three possible magnetic measurements must be present. Columns are delimited by a single unique character (typically a comma or a tab). You are first prompted for the data file and then you may enter the positions of the different data columns and the kind of delimiter to use. Enter a "0" for data types not present in the file (X and Z must be present).