Complex sentence: Labor retained power in 1975 with a majority of seats but lost the two-party vote on 49.2 percent, which saw Dunstan institute "one vote one value" electoral reform, which meant that all electorates had to contain approximately the same number of enrolled voters.
Split into simpler sentences: Labor retained power in 1975 with a majority of seats but lost the two-party vote on 49.2 percent. Dunstan then instituted "one vote one value" electoral reform, which meant that all electorates had to contain approximately the same number of enrolled voters.