The Big Mac Index is published by The Economist as an informal and light-hearted way of measuring the purchasing power parity (PPP) between two currencies and provides a rule of thumb to see the relative cost of the same item in different countries.
If you want to buy a Big Mac, look how much it is in Switzerland compared to Egypt. How to use this? Think of retirement. If you are in the US with $1 take it to Egypt and it goes 3.5 times as far ($1 in the US is like $3.5 in Egypt).