High Quality Content by WIKIPEDIA articles! Rail transport modelling utilises a variety of scales (ratio between the real world and the model) to ensure scale models look correct when placed next to each other. Model railway scales are standardized worldwide by many organizations and hobbyist groups. Some of the scales are recognized globally, while others are less widespread and, in many cases, virtually unknown outside their circle of origin. Scales may be expressed as a numeric ratio (eg: 1/87 or 1:87) or as a letter defined in rail transport modelling standards (eg: HO, OO, N, O, G, TT and Z.) The majority of commercial model railway equipment manufacturers base their offerings on NEM or NMRA standards in most popular scales.