The structure of the card number varies by system. For example, American Express card numbers start with 37; Carte Blanche and Diners Club with 38. American Express - Digits three and four are type and currency, digits five through 11 are the account number, digits 12 through 14 are the card number within the account and digit 15 is a check digit.
The model is the most basic element of the scientific method. Everything done in science is done with models. A model is any simplification, substitute or stand-in for what you are actually studying or trying to predict. Models are used because they are convenient substitutes, the way that a recipe is a convenient aid in cooking.
Models vs Theories. Scientific studies and discoveries come about after a well-thought-out hypothesis and thoroughly conducted experiments that produce models and theories. Students may have encountered countless models and theories of infamous scientists who once aimed to explain the different phenomena. There may also be classes where teachers or professors ask the students to formulate their own model and/or theory to draw the difference between the two.