The program will use the *y* errors you enter only to calculate the reduced chi-squared
(which should be "near" 1). The program reports errors in the parameters of the fitted function
by stretching or shrinking the *y* errors you entered until the fitted function goes through
most of the error bars (i.e., until the reduced chi-squared is 1). Thus if you have no idea
what *y* error to enter, little harm results by just using the default value of a constant
*y* error of 1. Nevertheless, an important part of any lab is reporting
and *justifying* an estimate of *y* error. You should demonstrate an ability to
recognize and numerically evaluate the less-than-perfect nature of all measuring instruments used.
On the other hand, do not be alarmed if your reduced chi-squared is not near 1: this happens
frequently in introductory labs. You should be alarmed if
you cannot justify your estimate of *y* error (even if your reduced chi-square is
exactly 1).

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