The Duckworth-Lewis (DL) system was developed by two UK mathematicians, Frank Duckworth and Tony Lewis, to resolve the problem of adjusting second innings targets in rain-reduced limited overs matches in an equitable manner.
Previous systems in use in both international cricket and domestic competitions around the world tended to favour either the batting or the bowling team to, at times, an extreme degree. In the early 1990s, Duckworth and Lewis set out to develop a fair system to both teams in all circumstances.
They did this by collating the scores from every one day international ever played, and this data was used to develop models that used overs remaining and wickets in hand as 'resources'. The latest version of the system, now known as Duckworth-Lewis-Stern (DLS) since mathematician Steven Stern took over the reigns after Duckworth and Lewis retired (Version DLS20, 2016), is now used in One Day International, Twenty20 International, and domestic & national tournaments limited overs cricket. Despite its statistical complexity, the actual use of the DLS software is very easy and training is provided to umpires and scorers.
In New Zealand, the two Official Scorers at both One Day and Twenty20 matches, at all levels of cricket under NZC jurisdiction, produce the DLS par score sheet, which is then circulated to umpires, coaches, captains, and others as required.