U.S. companies command an average enterprise value to earnings before interest, tax, depreciation and amortization multiple of 7.5 times, according to Citigroup.

The depreciation of some 25% in sterling's trade-weighted value from mid-2007 had kindled hopes that an export boom and an import slowdown would bolster GDP growth.

For those who would like to extend this to a more sophisticated model, consider adding in depreciation and the time value of money.