Like a bicycle chain
https://www.google.ca/search?q=chai...3DLDSiQK8z4HoCA&ved=0CFwQsAQ&biw=1024&bih=378
http://professionalwatches.com/2009/02/academia-tourbillon-force-cons.html
Academia Tourbillon Force Constante à Chaîne by DEWITT
February 9, 2009 | Baselworld, DeWitt
DeWitt-Constant-Force-tourbillon.jpg
DeWitt has enhanced its legendary constant force tourbillon with a system that relays energy to its associated power reserve indicator. Rotating the crown when winding the barrel-spring drives a miniature chain, which uses an intermediate wheel to activate the power reserve indicator sliding on a worm screw. Three years after developing an ingenious patented regulating system - three extra wheels transmitting impulses of identical force to the tourbillon, whatever the barrel's degree of tension - DeWitt has now taken innovation to even greater heights.
DeWitt-Constant-Force-tourbillon-2.jpg
Technical Specifications:
Movement
Manually-wound, DW8050 calibre, tourbillon with constant-force device, 25 rubies, 21,600 vib/h, 72-hour chain-driven power reserve, flat balance-spring
Functions
Hours, minutes, power reserve indicator
Case
950 platinum, 43 mm
Sapphire crystal front and back
Dial
Black with Côtes de Genève decoration
Opening over constant-force device at 8 o'clock
Opening over tourbillon cage at 5 o'clock
Rail power reserve at 10 o'clock
Bracelet/Strap
Black alligator leather with 750 platinum folding clasp
Time out
Booker