The MDI based version of the tool is described in

Falconer, D.A. Barghouty, A. F., Khazanov, I., and Moore, R.L., 2011, "A Tool for Empirical Forecasting of Major Flares, Coronal Mass Ejections, and Solar Particle Events from a Proxy of Active Region Free Magnetic Energy", Space Weather 9 S04003.

The work on the development of a free-energy proxy that can be applied to line-of-sight magnetograms is described in a series of papers:

Falconer, D.A., Moore, R.L., and Gary, G.A., 2002,Correlation of the Coronal Mass Ejections Productivity of Solar Active Regions with Measures of Their Global Nonpotentiality from Vector Magnetograms: Baseline Results", ApJ 569, 1016.

Falconer, D.A., Moore, R.L., and Gary, G.A., 2003, "A measure from line-of-sight magnetograms for predicting coronal mass ejections", J. Geophys. Res. 108 (A10), 1380.

Falconer, D.A., Moore, R.L., and Gary, G.A., 2006, "Magnetic Causes of Solar Coronal Mass Ejections: Dominance of the Free Magnetic Energy of the Magnetic Twist Alone", ApJ 644, 1256.

Falconer, D.A., Moore, R.L., and Gary, G.A., 2008, "Magnetogram Measures of Total Nonpotentiality for Prediction of Solar Coronal Mass Ejections from Active Regions of Any Degree of Magnetic Complexity", ApJ 689, 1433.

Falconer, D.A., Moore, R.L., Gary, G.A., and Adams, M. 2009, "The Main Sequence of Explosive Active Regions: Discovery and Interpretation", ApJL 700, L166.

Falconer, D.A., Moore, R.L. Porter, J.G., Gary, G.A. and Shimizu, T., 1997, "Neutral-Line Magnetic