Enter values, hit a button
H
o
Omega
M
z
Omega
vac
Open
sets Omega
vac
= 0 giving an open Universe [if you entered Omega
M
< 1]
Flat
sets Omega
vac
= 1-Omega
M
giving a flat Universe.
General
uses the Omega
vac
that you entered.
Source
for the default parameters.