Image source, Huw Evans Picture Agency
Glamorgan have spent just two seasons in Division One, in 2001 and 2005, since the system was introduced at the turn of the century.
ByNick Webb
BBC Sport WalesAtCentral Co-op County Ground
Rothesay County Championship Division Two, Central Co-op County Ground, Derby (day four)
Glamorgan 259 (88.3 overs): Carlson 94; Reece 4-67, Dal 3-29
Derbyshire 17-0 (5 overs)
Derbyshire 11 pts, Glamorgan 9 pts
Glamorgan all but sealed promotion to the top flight of the Championship for the first time in 21 years as their match away to Derbyshire ended in a soggy draw.
Rain washed out the third and fourth days, while high winds prevented any play on the first day, leaving Derbyshire with little opportunity to cut Glamorgan's lead in second place.
With Gloucestershire failing to get batting bonus points, that leaves only Middlesex with any theoretical chance of overhauling Glamorgan in second, and the Londoners are on the back foot on the final day against Lancashire.
The Welsh county have won five Championship games and are unbeaten since April, while Derbyshire are set for their best four-day finish since 2014.
Glamorgan earned their success with a run of three successive wins in May, over Kent, Northants and Middlesex, followed by the double over Kent in July and victory away to Lancashire in August.
Derbyshire needed bright skies on the fourth morning to have any chance of forcing a win or gaining more bonus points to take the race into the final week of the season.
But further rain during the morning led umpires Steve O'Shaughnessy and Suri Shanmugam to call play off at 12:20 BST.