Short answer
The replica Cartier Astrotourbillon 42mm copies a Cartier design where the tourbillon carriage sits at the center of the dial instead of at 6 o'clock. On a good replica the carriage turns one full circle every 60 seconds, the arm that carries the balance acts as the seconds indicator, and the case measures 42mm across without the crown. If the carriage spins faster than that, or the dial print looks flat, the watch is a low grade build. Check those three points first, then look at the rest.
What you are looking at
The original Astrotourbillon uses a caliber built around a central carriage. The balance wheel rides at the end of a long arm, so the whole assembly sweeps the dial like a hand. Cartier calls the shape of that arm a comet. A replica in the 42mm size has to reproduce the open dial, the applied Roman numerals that stay on the outer ring, and the gap in the middle where the carriage passes.
Most 42mm replicas use a modified automatic movement with a decorative carriage on the dial side. It turns. It does not regulate the rate the way a real tourbillon does. That difference matters less on the wrist than whether the carriage geometry looks right in proportion to the dial.
Specs to confirm
- Case: 42mm diameter, roughly 12 to 13mm thick, sapphire crystal front and back on better builds.
- Carriage: one rotation per minute, arm aligned to the 12 o'clock marker when the seconds read zero.
- Dial: open center, Roman numerals in the correct Cartier font, no fuzzy edges on the print.
- Hands: blued steel finish, correct length, no paint flaking at the tips.
- Strap: alligator grain leather, 20 to 22mm at the lugs, matching buckle.
How to inspect one before you pay
- Ask for a video of the running watch with a clock or timer in the frame.
- Count the carriage rotations against the timer. One turn per minute is correct.
- Ask for a photo of the caseback engraving in raking light.
- Check the lugs and case sides in that photo for tool marks or uneven brushing.
- Ask for the measured case diameter with calipers next to the watch.
- Confirm the strap width at the lugs matches the buckle width.
- Request a short clip of the crown action at each setting position.
Wear and care
At 42mm this watch sits large on a 6.5 inch wrist and about right on a 7 inch wrist. Keep it away from magnets, since the carriage sits close to the dial and a magnetized movement will run fast. Set the time with the crown out and the hands clear of the carriage. Store it in a case with the strap relaxed, not wrapped tight around a pillow. Clean the crystal with a microfiber cloth. Have the gaskets checked before you swim, and assume no water resistance beyond splashes unless a tester confirms it.