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).
The standard SIM is the most common SIM card used in mobile phones today. Measuring around 1â long by 0.6â wide it is the largest of the three SIM cards. The micro SIM is half the size of the standard SIM measuring around 0.6â long by 0.5â wide.