On Oct. 13, EMC stock closed at $27.55 vs a Dell offer price of $31.74 (adjusted for VMware's closing stock price) and an assumed undisturbed price - the average closing price in September - of $24.06.

The calculator assumes that the shortfall from Dell's offer results from some combination of (a) uncertainty the acquisition will complete and (b) a discount in the value of the proposed VMware tracker stock compared with actual VMware stock.

At 100 pct probability of the deal closing, for example, all the shortfall - $4.19 per EMC share - is attributed to the tracker stock.

The underlying VMware stock is worth $7.69 per EMC share, so that's an implied discount of 55 pct.

Input a 75 pct deal probability, and the implied tracker stock discount is 30 percent.

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