The fact is,
θ0=π4
Sθi=π22+π23+...+π2i+1+θ02i=π22+π23+...+π2i+2
Si→∞θi=π22(1+12+122+...+12i...)
Si→∞θi=π22(2)
Si→∞θi=π2
So, the last correction is,
ϵi→∞=Mi→∞(1sinθi→∞−1)2tanθi→∞
ϵi→∞=Mi→∞(1sin(π2)−1)2tan(π2)=0
no matter what Mi→∞ and tan(π2) are. The smallest piece of π corrected is zero.