Using The Editor

The Edit Window
      After you have recorded data points for one or more curves, click the Stop button in whichever Record box you are using and return to the Main Control box.  Click on the Edit button to bring up digiMatic's  Editor.

      The coordinate values of the data points you have recorded are displayed in a scrollable window.  The number of this curve, the total number of curves, and the number of points in this curve are displayed above the list.  You may change the precision of the values displayed from zero (integer) to four decimal places using the precision selection boxes provided.  You may edit the X Axis and Y Axis headers or the data values by clicking on any line and changing the text in the X: and Y: edit boxes at the lower left.
      Clicking on a line of data selects the data pair and the Delete button activates.  Clicking the Delete button will remove the selected data point from the set.  You may shift-click to select a range of data values just as you would in a word processor to select a range of text or in a spreadsheet to select a range of cells.  Clicking Delete with a range of data values selected will delete all points in the range.  Should you select all data points, including the headers, and Delete, the entire curve will be deleted and the number of curves in the current set will decrease by one.  If you select and delete just the X Data - Y Data header in curves 2 or higher, but not the data points, the data values will be concatenated onto the previous curve without sorting.
      A special type of deletion process is allowed if you select any data point and hold down the command key while clicking the Delete button (1-Delete).  You will be presented with the dialog below.  Typing in a number and applying "Save every nth point..." causes digiMatic  to keep the first, last, and every nth point in the data set(s) and delete all other points.  This is very useful for reducing the number of data points in an AutoScanned curve prior to exporting the data to a graphics program.  Often, a reduced number of data points makes it easier to fit smooth curves to the data.

      View the next curve in the set by clicking the Next button and the prior curve in the set by clicking the Prev(ious) button.  If your data set contains lots of data points, it may take a second or two for the list to appear whenever you switch from one set to another.
      When the Editor first opens, the Sort X button will be activated.  Clicking on the Sort X button causes the data values in all data sets to be sorted in ascending order according to the X values and redisplayed.  This is a relatively fast operation but it may take two or three seconds if you have hundreds of data points and several sets.  The Area button is activated whenever a Sort is completed.  We'll discuss use of the Area button in a moment.
      If you have finished using the Editor, click the Done button to return.  You may enter the Editor at any time after recording at least one point with digiMatic .  After returning to the Main Control box, you may digitize more points, add curves, change options, go out to lunch, answer the phone, wash your socks, and still return to the Editor again.

Calculating The Area Under Curve Segments 
      As soon as a sort is completed, the Area button is activated  When you click the Area button, digiMatic  will calculate the area under each curve in the set and display the areas in a pop-up box like the one below.  The area is calculated using either Simpson's Rule or the Trapezoidal Rule depending on which radio buttion you have selected in the Editor.

If you click the Save button in the Area List box, you will get a Macintosh File dialog that will allow you to save the values in this list to a tab-delimited text file.
      The areas that are calculated are numerical approximations of the integral

The Trapezoidal Rule approximates the area by summing the areas under successive trapezoids formed by connecting each pair of data points with a line and dropping verticals to the X axis from each Y value.
      This figure illustrates one area segment from such a calculation:

The Trapezoidal Rule calculation is extremely fast and gives an good approximation of the area when curve segments are relatively smooth and straight or if there are lots and lots of points along the curve.
      For many curves, especially chromatograph peaks and the like, a much more accurate approximation for the area is given by Simpson's Rule.  This algorithm requires as input an odd number of data points at evenly spaced values of X.  Clearly, it is a little much to expect you to figure out some way to get a list of data points that meets this requirement, so we use a special interpolation algorithm before using Simpson's Rule in order to convert the data points in your list to a proper input list.  This is done by "sequential polynomial interpolation".  Essentially, we march along the curve you send to the area calculation and successively fit 4 of the data points at a time with a polynomial.  New Y values at 199 evenly spaced X values along your curve are calculated from these successive fits and used in the Simpson's Rule calculation.  The Simpson's Rule algorithm does all of these calculations for you.
      These 199 data points can sometimes be used as a "curve fit" to your data set, especially when you have some points that are relatively widely spaced in the original data.  To save the list of interpolated points to a text file, hold down the command key and click the Save button in the Area List box.  A Macintosh File dialog appears.
      If you have lots of data points in a set, the Simpson's Rule algorithm has to do a lot of number crunching to get the area.  Because of this, we have built into digiMatic  the ability to determine if your computer has a Floating Point Unit installed (FPU, math coprocessor, 80881, 80882 are other monikers).  If so, digiMatic  uses the math chip to perform the calculation.  With a math chip, it will only take 5-10 seconds of computation time for even the largest of data sets.  If, however, you are using digiMatic  on a Mac Plus, SE, or Classic and have no FPU, the Simpson's Rule calculation could take 2-3 minutes or more.  Consider 1) using the Trapezoidal rule or 2) finding lunch.