These photos show the relative sizes of locomotives in the most popular modeling scales.  From left to right, the scales are: G, O, HO, and N.
 
 
 

Settling occurs when the paint pigment falls to the bottom of the bottle.  All paints tend to settle when they haven't been used for a while.  Modeling paints are notorious for settling while you use them the end result being that the color you finish painting with is not exactly the same as the color you started with. 
Use the following trick to maintain a consistent color while painting.

Trees

Most modeling pieces come in trees.  If you think of the specific modeling piece as a leaf it is attached to a tree trunk via a branch.  Most modeling trees are numbers so they can be easily referred to in the instructions.

 The Modeling kits available at the store range from basic to advance.  Depending on the manufacturer the item skill levels can range from 1-3, 1-4 or 1-5.  For modeling tools we have two major manufacturers available Zona or Excel.