Gaborone  - Before entering the world's largest diamond sorting facility in Gaborone, you have to check your chewing gum at the door - lest you be tempted to stud it with a stone.

You may also be asked to turn out your pockets, show the soles of your shoes and empty out your pen to prove you aren't concealing a gem.

But routine searches are a thing of the past at the Diamond Trading Company Botswana (DTCB), a joint venture between the government of Botswana, the world's largest diamond producer, and Debswana - itself a joint venture between the government and mining giant de Beers.

Instead of hands, there are 100 security cameras constantly scanning workers and visitors for sticky fingers.

And every gem - or nearly - is accounted for by weight. If the weight of the box of rocks a sorter returns at the end of his shift doesn't exactly match the box he or she was given at the start of the shift, the building is locked down and no-one allowed leave until the missing stone is found.

Don't even think about making a dash for it. The sorting area is separated from the exit by a bewildering array of centrally- controlled security doors, portals and turnstiles.

Not to mention the hawk-eyed security guards. At the end of a recent shift, the guard appointed to tail the German Press Agency dpa - every visitors gets one - spotted a speck on the floor under a sorting bench no bigger than a large grain of sea salt. The stone weighed only 0.09 carats but was worth between 300 and 400 dollars, according to company spokesman Kago Mmopi.

The last attempted robbery at the DTCB took place over 20 years ago when it was still located in central Gaborone, according to DTCB managing director Brian McDonald.

The employee was caught, thrown in the dock that very afternoon and sentenced to six years in prison.

"I think that sent a strong message," he says.

Above-average pay packages also help to keep workers on the straight and narrow. The starting salary for a sorter at the DTCB is 6,000 pula a month (902 dollars a month) plus free healthcare, subsidized accommodation, healthcare and help with mortgage repayments. (dpa)