Generally you only need to store one value in your table if Number and Name are linked. For example, if customer 555 was always "Joe Smith" then you just need to store 555 in your second table. This is the basis of a relationship between two tables (customers and, say, orders). I cover this in Access Expert 1 and 2.

The only time you would need to store BOTH values in your table would be if you could change one of them without the other. For example, if you want to enter a product ID and still be able to edit it's description. For example product 678 is "Cotton Sweatshirt" but you want to be able to change the description to "Cotton Sweatshirt, Large, Blue." But even in that case I would still recommend a 2nd options field. You do this with a DLookup and AfterUpdate event.