AMONG the many mysteries surrounding the flight of Malaysian Airlines Flight MH370 there are two conclusions to draw. It shows how much the digital world can reveal our movements, and it shows the limitations of the digital world.

If we only had physical evidence to go on, the search parties would still be concentrating on the South China Sea and possibly the area to the west of Malaysia, because the only clues they would have would be the radio silence at the border of Malaysian air traffic control area and the military satellite track.

It would never have occurred to the search parties to even consider the Southern Indian Ocean. It is only because an electronic device on board the airliner was periodically pinging a satellite high above that we now have strong grounds for believing it is in a completely different part of the world, seven hours' flight away.

Likewise, if you make a call or send a message with your mobile phone, the signal will reveal your location to trained analysts, or at least put you within an area which is considerably smaller than the area denoted by the aircraft's pinging device. Every time you take your mobile phone with you when you leave your house, you are leaving a digital breadcrumb trail behind you, just as the missing aircraft did. Unlike real breadcrumbs, these traces don't disappear. Computers, like elephants, never forget. Even if you delete a file, it is possible to reconstruct it if you know enough about how computers work.

Unlike the process of decoding an airline's pinging device, the techniques in decoding a mobile phone's location are so well known and so widely used that detectives routinely seize suspects' mobile phones and analyse them to find out where their owners have been. It's a bit difficult for a defendant to convince a jury that they were in bed with their girlfriend and nowhere near the scene of the crime, when their mobile phone is logged as being right there at the material time.

But computer records, however permanent have their limitations. They are in the end, just a series of 1s and 0s sent by one electronic device to another. Just because a mobile phone was at the burgled house at the time its burglar alarm went off, doesn't mean that its owner was with it, as defence barristers never tire of telling juries.

It is not surgically attached to its owner's wrist. It is possible that someone stole it or the owner lent it to a friend who then decided to burgle a house without telling him. But the digital records do place the onus of the owner to show that he or she wasn't with it when it strayed into dangerous territory - and if the police found it in the defendant's pocket on arrest, he or she has got big problems.

It's the same with the electronic device on the aeroplane. We still don't know definitively that the airliner ditched. What one computer can do, another can copy. It is possible that the electronic device periodically saying "Hi" to a satellite on a southbound journey to nowhere wasn't on the missing aeroplane at all, but was on something else with wings that was masquerading as the missing aeroplane, for reasons unknown.

Being human beings and not computers, we need something more than a series of 1s and 0s, however skillfully interpreted. We need something physical that is nothing to do with the digital world. Only then can we really believe what the experts are telling us, that Flight MH370 went so far off track. So until an irrefutable piece of Flight MH370, preferably with the aeroplane's identification, is on board a ship en route to inhabited land, the passengers' families will desperately cling to hope.

How computers used to be: The rebuild of a Mark 2 Colossus at the National Museum of Computing