Plotting raw data and function on same set of axes - Mathcad 15

Without your worksheet it's hard to guess exactly what goes wrong.

You should either make sure to evaluate your function on each of the experimental (x-axis) points, or use a separate running variable for plotting the function:

Above is the separate running variable. Below uses the x-data points from the data table:

Success!
Luc

If you use a new entry on the y-axis it needs a corresponding entry on the x-axis. If ther is none, the last one on the x-axis is used instead.

So from your description I guess you have a function lile f(x) and a vector od y-data values on your y axis. That way you would need an independent variable x (either use quickplot or define x as range) AND a vector of  x data values on your x-axis.

An alternative, which was also shown above, is to use only the data value on the x axis, lets say its X, and use Y and f(X) (eventually you need to vectorize that call) on the y axis. You will lose the intermediate values of your function that way, though,as it sill aonly be evaluated at your data points.

BTW, it would have been a good idea if you had attached your worksheet so we would not have to guess what exactly you did wrong.