The electronic detonator, instead of having a pyrotechnic delay (effectively a chemical burning reaction which has a certain time to burn), incorporates a chip inside the detonator.
Back in the mid-1970s, Orica (and indeed back through ICI and ICI affiliates which were the predecessors of the Orica group) began development of an electronic blasting system to try and improve on the accuracy being achieved at the time with pyrotechnic delays. While these were the standard industry method for timing delay detonators, they were, nonetheless, subject to anywhere from a 1% to 10% variation.
According to Mr Bullis, the accuracy of these units is better than [+ or -]0.1% of program delay -- comparable to 1 - 10% for standard pyrotechnic delays, or an order of magnitude improvement.