voltage below 2 V on MSI-5187 ?

a few years ago I saw a web page that showed jumpers for down to 1.4
V
now I can't find this infor again.
MSI manual only shows 2 to 3.5 V but there is a fifth jumper
on these socket 7 boards, usually the jumpers form a binary number,
V = 2 + binary/10
I have another where the fifth bit is a sign bit and it goes below 2 V
(although that mobo documentation only showed three possibilties below
2 V)
now I don't want to experiment and get 1.9 V when I want 1.6 V
[for a K6-3+ embedded low voltage - rather rare]
Does anybody know what the setting are?
Perhaps it is only for a later revision of the mobo?