Elliott Wave (1) and (5)
Elliott Wave (1) and Elliot Wave (5) are very often equal in Price.
If Wave (3) is the extended wave (i.e. it is the longest Wave) then very often Wave (1) and Wave (5) tend to be approximately equal in price.
As wave (5) is very often equal in price to Wave (1), once Wave (4) is complete, this allows an easy way to approximate where the Wave (5) will end.