Hydrodynamic Radius extraction manually

Hello,

In our Lab we have a Delsa instrument, it's nice, but I did not find how to get Hydrodynamic radius manually from the correlation curve. I don't want to get it automatically, I want to get it from the correlation curve. So how can I do it please? Because automatically, it's giving a very strange PDI (2.893e-09).

many thanks,

Amira