Select the well(s) to be used in to calculation from the list, or by dragging out an area on the map.

Specify any options, such as polygons, depth units and sources for the tops. 

Specify an Output Name for the formation by typing in a name or select a name that already exists.

Specify a Type from the drop down menu for the top and a source by typing in a source or selecting from the drop down list.

Create an expression for the calculation. You can create any expression using a top, formation alias, or number as input. Every time you need to use a top as input, select the top name from the Variables drop down.