Interesting quote bit of info also found on the Wikipedia entry ....
"The instrument's ancestry is traced to the Hawaiian Islands in the late 19th century after the Spanish guitar was introduced there by European sailors and by Mexican vaqueros who came there to herd cattle. Hawaiians who perhaps did not want to take the time to learn how to play a Spanish guitar, re-tuned the instrument so it sounded a major chord when strummed, then thought to be an "unorthodox tuning" . This was known as "slack-key" because some of the strings were slackened to tune to a chord. To change chords, they used some smooth object, usually a piece of pipe or metal, sliding it over the strings to the fourth or fifth position, easily playing a three-chord song. To make playing easier, they laid the guitar across the lap and played it while sitting. The problem with playing a traditional Spanish guitar this way was that the steel tone bar strikes against the frets making an unpleasant sound unless played very lightly—this was corrected by raising the strings higher off the fretboard with a piece of metal or wood over the nut. This technique became popular throughout Hawaii."
https://microtonal.m.miraheze.org/wiki/Pedal_steel_guitar