A1 Height1 Height2 Height3 Height mean
B1 157.6 157.7 159 ?

I need a formula that will average the two closest figures and ignore the
third figure. eg Height 1 and Height 2 are closest therefore average these
two but ignore Height 3. It won't always be that height 1 and 2 are are the
closest. It could be that height 1 and 3 are closest or height 2 and 3 are
closest.

Help?