Computation units
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Currently, the number of computation units deducted from your Session Id when you run 
CSubtract (i.e. MnCSubtract) is 
(a) programmatically: the following number or derived using the following formula: 1.
(b) interactively: 30 less than (a), subject to a minimum of zero. If the units deducted exceed zero then you will need a 
SessionId to complete the calculation.