[FOM] analysis with hyperreals vs. surreals?

[Steven Obua]

Ben Crowell wrote:

>I'm studying Conway's On Numbers and Games, and he has some brief but
>intriguing remarks about doing analysis with the surreals, and about
>how the surreals compare with the hyperreals. 
>
Could you point out where in Conway's book this comparison of surreals 
and hyperreals happens?

In the mechanical proof-assistant Isabelle both the hyperreals and 
partizan games (the stuff out of which surreals are made) have been 
formalized, and I would like  to formalize the connection between them, 
if there is any. Unfortunately I don't know the connection, can someone 
provide links?

Steven Obua