Elite Novo Force 8 - resistance levels

[robv]

I'm a new and happy user of the Elite Novo Force 8. According to my (limited) experience the resistance setting of 3 corresponds to riding my bike on a flat road. Settings 4-5-6-7-8 emulate an uphill gradient, settings 1-2 are downhill. Is there a rule of thumb for the relation of the settings to an actual gradient? I mean, what are the (approximate) uphill gradients for setting 4-5-6-7-8?