What does "baker's dozen" signify?

Regular dozen is twelve, but a baker's dozen is 13. Years ago in England there were strict penalties for those who gave short weight. During this era Bakers were usually not educated and terrible counters. So to avoid any penalties, the bakers would give 13 instead of 12 or a dozen, just in case they miscalculated. Am i right?

a bakers dozen is 13 one over the usual twelve. This developed when a baker would bake a batch for an order and would generally bake a test piece first hence 1 dozen plus one test piece is 13 a bakers dozen