Which specific, bright star-forming region was used as a beacon to measure the distance to the Perseus Arm?

Answer

W3OH

International astronomers used the methanol maser source known as W3OH, located within the Perseus Arm, to achieve highly precise distance measurements.

Which specific, bright star-forming region was used as a beacon to measure the distance to the Perseus Arm?
galaxyastronomyDistanceEarthMilky WayPerseus Arm