A general rule of thumb is that if your economic model has no value judgements, it's positive economics, and if it does have value judgements it's normative economics, since to tell someone what he ought to do, you first have to judge what is best for him.
A subscriber identity module or subscriber identification module (SIM) is an integrated circuit that is intended to securely store the international mobile subscriber identity (IMSI) number and its related key, which are used to identify and authenticate subscribers on mobile telephony devices (such as mobile phones and computers).
Dimensions similar to those of a credit card. ID-1 of the ISO/IEC 7810 standard defines cards as nominally 85.60 by 53.98 millimetres (3.37 in Ã 2.13 in). Another popular size is ID-000 which is nominally 25 by 15 millimetres (0.98 in Ã 0.59 in) (commonly used in SIM cards).