Alternative Condition type is the formula Used For 
determining Condition Basis. 
For Example Absolute Discount can Be header discount which 
can be distributed among the line items as per cumulitive 
value opf ther items.
Alternative Calcultation type is  formula to the formula in 
the standard system that determines a condition.It is 
nothing but the routine used in pricing procedure.

Alternative calculation type , condition base values are 
used in pricing to meet the not so common business 
requirement .The normal pricing procedure can be mapped 
without using them .Coming to the alt cond type ,we have to 
use routines which stores the business logic and can be 
used against the relevant condition type as per the 
requirement .The routines ,in otherwords are the formulas 
that are defined in t-code VOFM by the ABAPERs based on the 
logic given by the functional consultants. Remember ,the 
routine is applied against a condition type in the pricing 
procedure .