If $p_{01}$ is the index for current year 1 on the basis of the year 0 and $P_{10}$ is the index for the year 0 based on year 1 then time reverseall test satisfy :

$P_{01}×P_{10}=100$ $P_{01}×P_{10}=10$ $P_{01}×P_{10}=0.1$ $P_{01}×P_{10}=1$

$P_{01}×P_{10}=1$