Modeling Japanese commuter trains: It's not quite N scale

I was looking for a stretch project in modeling Japanese commuter trains.  I think I got more than I bargained for.  The first thing that I realized is that I'm modeling in a non-traditional scale. 

Japanese commuter trains run on narrow gauge track. But, they are manufactured to run on 9mm n scale track. The off-the-shelf models from Kato and Tomix clock in at 1:150. That's just a smidgen larger than n scale at 1:160.

I looked up a 1:150 scale ruler and found one on Amazon. I ordered it, super pronto. 

Then . . .

I discovered that the ruler is in meters. I'll have to access my faded 7th grade memories and remember how to use the metric system. Maybe there's a YouTube video.