The plus and minus buttons of the navigator panel move the element selection through the periodic table according to an increasing or decreasing value of the index property.
	To select an index property: click on the drop-down arrow.

On the periodic table screen it is next to the index property window. On the property screens, the index property window is hidden, but the drop down button is at the right end of the navigation buttons.

From the scrolling list of index properties, select the property you want to index. The property values for each element are retrieved from the data file and the index order is calculated. The current element remains selected. Clicking on the plus or minus buttons will move the element selection to the element with the next greater or less value for the selected index property.