I'm thinking about my first Casio purchase and the model numbers are a bit confusing. These few watches look identical, except possibly the color. I have read that some of the letters are country codes, but what do the numbers mean. Prw2500-1A, prw2500t-7cr, prw2500-1b, and prw25001r-cr. Is there a place online that "decodes" the extensions. One more example are these two: Ga100c-8a and ga100LG-8a. Thanks in advance.