Of the 600-plus watches on offer at Antiquorum’s “Important Modern & Vintage Timepieces” auction on November 11 at the Mandarin Oriental Geneva, the top lot is not a Patek for once.

Instead, it’s an ultrarare Single Red Patent Pending Rolex Ref.1665 500m/1650ft—one of only six known.

Made in 1967 as a prototype for the legendary Sea-Dweller, the example on offer is thought to be one of only two known examples featuring a gas escape valve for deep sea diving.

One of the most important diving watches ever made by Rolex, it has never been seen before at auction.

That translates to a hefty estimate of up to about $128,000, or about as much as a a couple dozen pre-owned Submariners would cost.

But then you’d have to grow some more arms….