I've been using spritmonitor for years!
The 3.9 is slightly rounded up....if you check spritmonitor, you will find that they have 3.89 L/100 for my car, which is more or less 3.875.
Also, I haven't kept the MPG record here up to date, for the reason you cite. So I will delete my consumption record here and just use the US MPG icons from spritmonitor.
I have another car (Peugeot 405 DL) with over 325,000 km of fuel consumption records ar spritmonitor, and I'll be damned if I'm going to re-enter those data here!
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2008 Mercedes-Benz B 200
2006 smart fortwo BRABUS Canada 1 cdi cabriolet
2005 smart fortwo cdi pulse cabriolet
1966 Peugeot 404 Coupe Injection