To skeleton plot a sample onto a strip of graph paper, simply make marks according to the relative narrowness of each ring, as illustrated in the figure above. The graph marks range from no mark at all (not narrow) to a vertical mark of ten graph lines in length (extremely narrow). Note that rings #26 and #28 of the sample above are very narrow relative to their neighboring rings and that their corresponding marks on the 26th and 28th lines of the skeleton plot are eight to nine units long. In contrast to that, rings #16 and #19 are only moderately narrow relative to their neighboring rings and their corresponding graph marks are only five to six units long. Lastly, ring #5 is only marginally narrow relative to its neighboring rings and its corresponding graph mark is only 2 units long. Occasionally a notably wide ring occurs (e.g., ring #17 above), prompting dendrochronologists to mark a "b" (indicating big) on the corresponding vertical line of the graph paper.
Most of the other rings of the sample are merely average in width, and no mark at all is made on their corresponding vertical lines of the graph strip. Dendrochronologists typically accentuate narrow rings when skeleton plotting because narrow rings are consistently expressed by most, if not all, trees within a particular stand. Average rings are simply not marked on skeleton plots. Furthermore, it is not necessary for every dendrochronologist to skeleton plot a particular sample identically to succeed at crossdating, rather it is only necessary that the relative growth variation through time be consistently skeleton plotted with the relatively long or short marks.
When you skeleton plot with the applet, you are given a virtual increment core sample of tree rings extending from left to right through time as well as a virtual strip of graph paper. Make a normal mark on the graph paper by simply putting the mouse cursor on the correct vertical line and at the height (horizontal line) you desire and then click the left mouse button. Similarly, make a "b" mark by selecting the wide option when drawing marks. If you make a mistake, turn the eraser on and click over that (or any other mark you wish to erase). Don't forget to turn the drawer back on to continue making marks. You can also move the graph strip left or right by clicking and holding the left mouse button in the top part of the graph and moving the mouse.