Around 1979, Floyd D. Rose invented the "locking tremolo". This vibrato system became highly popular among 1980s heavy metal guitarists due to its tuning stability and wide range of pitch variation. The original Floyd Rose system was similar to the Fender synchronized tremolo, but with a number of extra mechanisms. The first and most obvious is a locking plate on the head nut, tightened with a hex key that fixes the strings at this point after tuning. This provides extra tuning stability, particularly while using the vibrato arm—but it also prevents tuning with the machine heads.