 Satellite services such as Sky Digital often offer regional variations by transmitting duplicate feeds of the same station for each region traditionally covered by groups of transmitters as an arguably costly way to provide regional variations within an area covered by the same satellite.Both the BBC and ITV do this, as do Channel 4 and Channel Five for advertisements.The digital set top box will determine which version of the channel to supply based on a list of post codes corresponding to the details on the user's smart card.