quattro[Moderator]
18141
Vacheron Constantin Monopusher Chronographs
All the models I could find with only one pusher to start, stop and reset the chronograph.
Enjoy!
A. VINTAGE MODELS
1/ Round case ref. 3307 (13 ligne caliber based on an ebauche by the brothers John and Charles Reymond - later known as the company Valjoux)

Model from 1927 made for King Alexander I of Yugoslavia (credit: Sotheby’s)

Model from 1929 with black hands (credit: goldammer.me courtesy of Phillips)
2/ Cushion case
a) Without pulsometer scale

Ref. 2990 ? (case n° 251050) from the 20s (credit: invaluable)

Ref. 2990 from 1930 (credit: Hodinkee)
b) With pulsometer scale

Model from 1928 with Stuart pear hands (credit: bexsonn.com)

Similar model with baton or sword (?) hands (credit: Horas y Minutos)


Similar model with B r eguet hands (credit: Davide Par m egiani)
B. MODERN MODELS
1/ Without tourbillon
a) Harmony ref. 5300S/000R-B055 with cal. 3300 (model launched for the 260th anniversary of the brand, in 2015)

(credit: Hodinkee)
b) Harmony ref. 5300S/000R-B124 with cal. 3300 (2016 edition of the previous model, with anthracite numerals instead of blue on the anniversary edition)

(credit: Hodinkee)
2/ With tourbillon
a) Harmony Ref. 5100S/000R-B125 with caliber 3200

(credit: H.M.Timepiece on FB)
b) Harmony Ref. 5100S/000P-B056 with caliber 3200

(credit: Horologium)

(credit: the watch observer)
c) Traditionnelle ref. 5100T/000R-B623 with cal. 3200

(credit: Watch I Love)
d) Traditionnelle ref. 5100T/000P-H041 with cal. 3200 (Collection Excellence Platine)

(credit: Watch Collecting Lifestyle)

(credit: Sjx)
3/ Split seconds
a) Harmony ref. 5400S/000P-B057 with cal. 3500/260

(credit: a blog to watch)
b) Traditionnelle ref. 5400T/000P-B637 with cal. 3500 (Collection Excellence Platine)

(credit: Sjx)
4/ Les Cabinotiers Minute Repeater Tourbillon Split-Seconds Monopusher Chronograph with cal. 2757 (there are 2 pushers for the chronograph on the right – one (at 2:00) for start, stop, and reset, and one (at 4:00) for the split-time function)

(credit: Hodinkee)