True calendar spread: Nov 2012 vs Dec 2012 [1.75]

Chart showing spread suggests 1.75 as effective split value for correcting calendar spread. Note that spread at close was 3.25 reflected by a pronounced spike. 1.75 is also median and type value of open, high, low and closing prices of 2nd, 3rd and 4th trading days before expiration.

Calendar spread Mon 11/12/12 to Thu 11/15/12 (chart/data by Linnsoft/eSignal)

Calendar spread vaules and statistical properties (data by eSignal)