Helpful Links

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Here is an online calculator to go between real life measurements and scale measurements: 

http://www.gardenstatecentral.com/scale_calc.html

Wikipedia List Railroad Reporting Marks:

en.wikipedia.org/wiki/List_of_reporting_marks:_A

T-Trak Wiki:

http://ttrak.wikidot.com/

 National Model Railroad Association:

 National Model Railroad Association (nmra.org) 

NMRA T-Trak Guidelines

 Considerations for T-trak Modules & Layouts 

HO Car Weight Chart