Short answer

326.10.40 is not an Omega reference number. Omega's Seamaster Aqua Terra 150M line uses prefixes such as 231.10 for the generation sold from 2008 to 2017 and 220.10 for the generation that followed. The string 326.10.40 appears in replica listings, marketplace titles, and image captions. No Omega catalog lists it. A watch sold under that number is a copy or a listing with a wrong reference.

How Omega builds a reference

Omega reference numbers encode case material, case size, and movement. Take 231.10.42.21.01.001. The group 231 marks the Aqua Terra family. The 10 marks stainless steel. The 42 marks the case size in millimeters. Later groups cover the calibre and the dial. The trailing digits of 326.10.40 do not match a published Aqua Terra family code, and 40 sits outside the case sizes Omega has published for the line: 34, 38, 38.5, 41, 41.5, and 43 mm.

Checks on a replica Aqua Terra

• Case size. Measure with calipers at the 9 and 3 o'clock edges. Copies run 0.5 mm to 1 mm under the stated size.
• Thickness. Copies of the 41.5 mm case run thicker than the genuine case.
• Dial. The teak lines on the genuine dial are cut deep and even. Copies show shallow lines and a soft edge at the date window.
• Date window. A genuine frame sits flush with the dial. Copies show a raised frame or a frame set off center.
• Movement. Calibre 8500 and calibre 8900 use twin barrels, a co-axial escapement, and a free-sprung balance. Most copies carry an ETA 2824 clone or a decorated Asian movement with a fake rotor and printed text on the bridges.
• Caseback text. The words Co-Axial Master Chronometer appear only on 2017 and later references with calibre 8900. A 231.10 reference with that text is wrong.

Serial numbers and paperwork

Omega stamps the serial on the movement and on the case. Both numbers must match. Boxes, cards, and hang tags are copied with ease, so paperwork carries little weight on its own. A Master Chronometer card carries a METAS number that Omega's database can confirm.

Price signals

A steel Aqua Terra 150M with calibre 8500 sells on the secondary market in the range of $2,000 to $3,500 for a full set. A price of a few hundred dollars points to a copy. Other signals: stock photos reused across listings, no photo of the movement, no photo of the serial, and one seller account that lists many brands.

What photos cannot show

Photos hide lume color, case bevels, bracelet flex, and the finish on the movement bridges. A loupe, calipers, and a timegrapher settle more than any listing image. If the listing carries 326.10.40, treat the watch as a replica until you see the movement through the caseback.