Editing 4 mm scale (section)

===EM gauge===
[[EM gauge|EM]] was originally defined to use 18mm as the track gauge (hence the name: Eighteen Millimetres). This was revised, and today EM gauge uses an {{RailGauge|18.2mm}} track gauge, which is closer to accurate but not fully to scale.  It was developed as an early improvement on the standard OO system.  It is still popular with FineScale modellers today because it utilises larger than scale flanges on the wheels of rolling stock, and because point and crossing (P&C) work is a little easier due to an overscale flangeway clearance.  These two concessions in scaling down the prototype make for reliable running.  This factor explains the continued popularity of EM as a scale for finescale modellers working today.