## Web-based Plotting for Physics

### Summary

For these *x*-*y* ('scatter') plots you need:

- Several (say
*N*) pairs of related data:
(*x*_{i} , *y*_{i} );
*i*=1,2,...,*N*. The choice of which variable is *x* (and which
is *y*) can be made on several bases:
- Which has the least error?
- Which is the controlling variable?
- What did your instructor tell you to do? (Note: if
you've been told to plot: "
*A* vs. *B*", *B* is on the
*x*-axis.)

- Ideally you should have an estimate of the accuracy of the
*x*
and *y* values of the data: the
so called *x*
and *y*-errors (*xe*_{i} and *ye*_{i} ). The accuracy estimate
may be a general rule (e.g., all the *y*-values are accurate to 3%) or individual
estimates for each datapoint. **The first thing you will be asked
is what sort of errors you have**. Making good estimates of errors
is perhaps the most difficult part of doing science, however it is not a
topic I've written on here: ask your instructor when in doubt!
- What is the current form of your data? Are the numbers already available on this
computer (for example in a spreadsheet)? In this case you can probably
just copy and paste that data into one of our bulk-entry forms. If your data
consist of numbers on a sheet of paper you'll be probably better off
using "pointwise" data entry -- in which case I'll want to know how many datapoints
you have (i.e.,
*N*). In either case, these web pages limit the number of
datapoints to *N*<100. Your errors may be in the form of a
formula
or a list of numbers.