Introduced in 1986, the Patek Philippe Grand Complications ref. 3970 perpetual calendar chronograph used a nearly identical aesthetic architecture of its iconic predecessors – the references 1518 and 2499. It used an all-new base movement, the caliber CH 27-70Q, which derived from the Lemania caliber 2310 – the same base movement powering early Omega Speedmasters. This was the first non-Valjoux movement Patek had ever used in a chronograph. The 3970 was sized at 36mm – a bit smaller than its direct predecessor, the ref. 2499 fourth series, which measured 37.5mm….