The difference is in the way the data are displayed in Logger Pro. When you look at the digital meter window, you are seeing a number that is the average of many readings taken between the times the display is changed. Noise is averaged out.

When you choose collect to start a graph, a point is plotted each time a reading is made (unless you have “Oversampling” on, see below). In short, you are probably seeing the raw readings while graphing and “smoothed” readings when looking at the digital (or analog) meter window.

You can also smooth graphed data, after it is collected, by going to Experiment/Data Collection and checking the Oversampling box. This will cause Logger Pro to average readings between times when it plots a point on the graph. Now, if you are collecting data very quickly, this will not make much difference (there is not time to take and average a lot of readings), but if you take data more slowly, the points plotted will be averaged considerably.

It is also possible to smooth data after it is collected by creating a New Calculated Column based on the original data and using SmoothAve (Smooth Average)or SmoothSG (Savitsky-Goley smoothing) as the function in the Expression for the New Calculated Column.