how I calculated
this is to multiply the edge of a particular situation by the probability of that situation occuring e.g. for 4 hands played
no tens seen : value = (5/43)(((35/51)^8)/13) = 0.044%
1 ten seen : value = (2/43)((16/51)((35/50)^7)/13) = 0.009%
total value = 0.044% + 0.009% = 0.053%
By the way perfect insurance does not mean you only take insurance when the dealer has a blackjack, in this case it would be worth 200%. It means to take insurance when the proportion of ten cards to none ten cards remaining is known to be greater than 1/3.