Enter your data in the "data" columns in the spreadsheet, label your axes using the entry fields (below the spreadsheet), and you will get a graph. Fit a line to your data by selecting a model from the choices in the middle of the page. Press the "Graph to Clipboard" button to copy your graph, and then paste it wherever you like.

• Entering and Copying Data
• Labeling and Scaling the Axes
• Choosing a Model
• Graphing Multiple Data Sets
• Using the Tangent Finder
• Annotating Your Graph
• Saving & Recalling Your Graphs
• Pasting or Printing Your Graph
• Superscripts, Subscripts, and Symbols

Manual Entry - Data can be entered by simply typing values into the data columns in the front panel spreadsheet. Numbers typed in the "±x" and "±y" columns will drawn as uncertainty bars on each data point. They are optional. You can navigate between cells using the arrow and enter keys. If you double click in a cell, you enter "edit mode" for that cell. In edit mode the left and right arrow keys move the cursor within a cell instead of between cells. The enter key and the up and down arrow keys take you out of edit mode. If the contents of a cell cannot be interpreted as a number, it will be colored red. If a number is very large or very small, it will be shown using scientific ("e") notation.

Pasting - Data can also be entered by copying a block of cells from a spreadsheet and pasting it in (via the ctrl-v paste command). nPlot will correctly parse a paste of one, two, or even four columns at once. Copying and pasting tab-delimitted data from a Word or Google document also works.

Bad Data - A suspect data point in an otherwise good data set can be ignored by checking its "skip" checkbox.

Swapping Columns - If you discover that you have accidentally typed your y data into the x column, just click the "Swap x & y" button. If you have any entries in the uncertainty columns, they will be swapped too. Holding down the control key while you press the swap button causes the axis labels to also be swapped.

Using Formulas - The indvidual cells understand math. If you enter 2+2, or 2*2, or 2**2, or 2^2, or 24/6, or 6-2, or 16^.5 the cell contents will be displayed as the number 4. The value is computed using the standard conventions for the order of operations. Placing the cursor in a cell recovers the original math, which allows for editing. (Double-click to enable the arrow keys inside the cell.) This can be very helpful in linearizing your data. For example, if you have measured something as a function of velocity and find that the best fit is a square law, you can then just add ^2 (or **2) at the end of each velocity entry to square it and plot your data as a straight line.

Clearing Your Data - Clicking the Clear Data button will clear the contents of the currently displayed spreadsheet. Holding down the control key while clicking it will clear all the sheets at once, as well as all the axis labeling and annotation. If you have selected a portion of your data, hitting the delete key will clear just that selected portion.

Copying Your Data - nPlot makes a terrible lab notebook. If you typed your data into nPlot first, but now want it somewhere else, you can highlight the cells you want to copy (using the usual click-then-drag method), and use ctrl-c to copy the data to the clipboard. The highlighting disappears as confirmation that it has been copied. From the clipboard, you can paste the data somewhere more permanent.

Labeling - To label the axes, just type your labels into the appropriate text inputs. There are separate inputs for the axis units (parentheses are automatically added). There is also a text input for an optional graph title. If you need superscripts, subscripts, or any special symbols (like Greek letters), see that section of the manual.

Scaling - It is (mostly) not possible to control the scaling of the graph axes. The auto-scaling routine is quite robust, and makes reasonable choices. If the data consists of very large or very small numbers, the axis labels will automatically be drawn using scientific notation. On the Settings menu you may choose whether to include the error bars when calculating the scale. The default behavior is to use the error bars so that they are never clipped. If you de-select this option, then the scaling will be calculated using only your data points, and the error bars may be clipped (this was the default behavior prior to version 5.90). nPlot will remember your choice (until the browser cache is cleared).

The Origin - By default, the point (0,0) is always included in the axes. This is done for pedagogical reasons, but you may have a data set where that is really inconvenient. You can turn off this default behavior in the Settings menu, but only for the current nPlot session. Next time you launch the program, the default behavior will be restored.

Select a Model - Choose a model to match your data by clicking on the list between the data sheet and the graph. The process that nPlot uses to draw the line on the graph is known as "fitting" a curve to the data, and the curve that results is called "the fit" for that model. The "results of the fit" are constants (between one and three of them) that do the best job of making the curve pass as close as possible to all the points in the data set, which is why what nPlot draws is known as "the best fit." Be aware that every fit from nPlot is technically a "best" fit. Your job is to choose the correct model.

Deciding Which Model - An objective measure of how well the fit agrees with the data is provided by the value of the RMSE, which stands for "root mean square error." It is essentially an average of the amount by which the curve misses each data point. The general rule (also a dangerous rule) is to choose the model that gives the smallest RMSE. The reason that this is dangerous is that a quadratic fit will almost always give the smallest RMSE, but it is almost never the correct model for the data.

Advanced Models - Some of the fitting models have been declared to be "advanced" and hidden behind the Advanced Models drop-down. (Probably you should not be choosing one.) These models are rarely seen in an introductory high school physics course, and the first two are actually advanced in that they require a "non-linear fitting method" (which has nothing to do with whether the best fit curve is a straight line). These models will only work if the majority of the data has positive values for both x and y. If no curve is drawn, it means that nPlot could not find a reasonable match between the model and the data. Since we are discussing advanced things, you should know that although the uncertainties in the data points are drawn on the graph, they are not used in the fits. Weighted fits are not for beginners.

The spreadsheet is actually five separate sheets, selected by the row of buttons (Sheet 1, Sheet 2, etc.) at the top of the data entry grid. Each sheet supports a completely separate fitting model and has its own plotting symbol and style of fitting line. They share a single set of axis labels, and the axes will be scaled to accomodate all curves at once.

The Tangent Finder does just what it says. When activated, it gives the slope of the fit at the x-value of the mouse position. By default, when the Finder is activated, the Lock To Data option is on, which restricts tangent finding to the x-values of the input data points. The x value and slope at that x value appear just below the tangent finder controls. The finder operates on whichever of the five sheets has been selected. If you want to include a tangent in your downloaded graph, slide the mouse off the top or bottom edge of the graph at the desired x-value.

Adding Fit Results and Notes - Clicking the Annotation button brings up the annotation menu, which will let you add information to your graph. For example, you can add the results of a fit as a block of text. The interface allows you to position that block anywhere within the graph. If you have more than one data set in your graph, you can position a separate block of text for each fit. To make it clear which block goes with which fit, you can add arrows that point from each block to the corresponding curve. If you change the model used on a data set, the annotation for the old model will automatically be erased. You can type text notes into the box on the Annotation Dialog and place them on your graph as well. If there is text in that text box when you add a fit annotation, that text will appear as the first line of the annotation. Notes can have subscripts, superscripts, and Greek letters.

Adding Max/Min Slope Lines - If you have a linear fit on any sheet, you can use the annotation menu to manually add additional lines to the graph. This feature is intended for students who need to draw IB style graphs. The completed line is drawn using dashes, and the slope and intercept are reported in the annotation dialog. If desired, this information can manually added to the graph using the Add Note feature. You can draw as many lines as you like, and although you cannot change a line after it has been drawn, you can remove it using the Edit feature.

Editing Annotations - The Edit button will throw up a list of all the added annotations. You can select any item from the list to reposition it. When your mouse is over an item in the list, the part of the graph that will be changed is highlighted in red. If it is a Note and not a Fit, you can edit the text first. Clicking on the "×" next to an item will delete it. If you have multiple data sets and multiple annotations, clearing the data from one data set deletes that data but not the related annotations. Delete them by hand using this editing function.

Saving - Your entire graph can be saved for later recall by clicking the Save Graph button. Type a name in the text input first, or nPlot will complain. If the name matches an existing saved graph, that earlier graph will be overwritten. There is no "are you sure?" warning! The graph is saved on your computer only. It cannot be accessed from any other device.

Recalling - If you click the Recall Graph button you will be shown a list of all the graphs saved in your browser. Click on a name in that list and the graph and data will be restored exactly as they were when you saved them. If nPlot detects that there is already data in the spreadsheet, it will ask before erasing your current graph and replacing it with the recalled one.

Deleting - If you hold down the shift key while clicking on a saved graph name, that graph will be deleted instead of recalled. You will not be asked if you are sure.

Impermanence - Your graphs are stored in the browser cache. If the cache is cleared for any reason you will lose all your saved graphs. Think of this graph saving feature as a convenience and not an archival record. Keep a copy of your data in e.g., a Google Sheet.

There are actually three separate ways to get a useful copy of your graph. Which one you should choose depends on what you want to do with the graph.

Open in a Tab - This option is designed for making a quick hard copy that you can tape into a real (made from paper!) lab notebook. Hold down the control key while pressing the "Graph to Clipboard/Graph in New Tab" button (the name changes when the control key is pressed). Your graph will appear by itself in a new tab. Print that tab to get a graph suitable for taping into a notebook.

Copy to Clipboard - Clicking the Graph to Clipboard button puts a copy of the graph in the system clipboard. From there it can be pasted into a document and printed. You can also paste it into the spreadsheet you are using as a lab notebook.

Download an Image - If you check the "Yes, download" radio button, then your graph will be downloaded as a graphics file (named using your axis labels as "y-axis_label_vs_x-axis_label.png") that you can use however you like. If you also select the "Include fit" radio button, you will get a second (plain text) file containing the fit results from all sheets (well, just the ones that have fits). If you request the text file, allow multiple downloads when you get the pop-up asking for permission.

Superscripts - To get a superscript in any text input (axis labels, units, plot title, or annotation notes), just precede the numerical superscript with the caret symbol "^". For example, to get v², type v^2. Superscripts are restricted to numbers only. All digits between the caret and the first non-digit character are assumed to be part of the same superscript.

Subscripts - Unlike superscripts, subscripts can contain (almost) anything you want: plain text, Greek letters, and superscripts. However, you have to tell nPlot when the subscript starts and when the subscript ends. Subscripts start with "_{" and end with "}". For example, typing F_{net} gives F_net. There are some restrictions. Subscripts may not have subscripts, and if your desire is to have curly brackets as part of your subscript text, that is guaranteed not to work right.

Greek and Other Symbols - To get a Greek letter, type a backslash "\" followed by the name of the Greek letter. For example, type e.g. \Delta, \delta, or \mu to get Δ, δ, or μ. If an uppercase Greek letter is the same as a character in the Roman alphabet, no translation is made. Disappointingly, typing \Alpha just gives \Alpha, not the A you were hoping for. To make it easier to read what you are typing, the first blank space between the Greek letter and the rest of the text is ignored. If actually want a space after the Greek letter, type two spaces in your input. For example, both "\DeltaL" and "\Delta L" will print as ΔL, but "\Delta L" will print as Δ L.

Special Characters - The Greek symbol processor also understands a few special characters (which means the same business about spaces applies). These characters are \deg (°), \times (×), and \sqrt (√ ).