The single-push corrector first appeared in Lange's first perpetual, the Langematik Perpetual, which was introduced in 2001 in platinum (310.025) and yellow gold (310.021). But it was practically a secret. Lange didn't advertise or promote this wonderful feature. That made "discovering" it even more special. At the time, I remember wondering if a one-push corrector was typical for perpetual calendars across other brands. Then I found out that it was atypical.