Recently a poster in the Omega Forum mentioned four potential criteria for spotting c.321 Speedmasters: The presence of a non-Moon case back (just a simple engraved seadragon)? No 'Professional' on the dial? The no crown guard style case? The metal applied Omega symbol on the dial? The answer is: none of the above! These items are possible indications of the presence of a c.321 but none of these guarentee that the c.321 is "under the hood"... For Example: This item is posted for sale on a well known watchseller's site: This item is posted for sale on a different watchseller's site: Figure 1 Figure 2 Omega - Speedmaster - Pre Moon - Stainless Steel - No Crown Guard - Near Mint ++ - 17 Jewel Manual Wind, CAL 321, Black Dial, Silver Handsand Luminous Markers, Round Pushers, Signed Crown, Screw Back, 40 1/2mm Case, Stainless Steel Omega Bracelet, Completely Serviced, 90 day service warranty, Priced at x,xxx.xx   Omega - 17 Jewels,3 register, early 60's type movement,functions well,in PERFECT condition., excellent+ Waterproof SS, round pushers,60's Speedmaster, Man on the Moon, case and Omega bracelet Condition PRISTEEN!!, mint+ ORIGINAL Omega Speedmaster Black Mat with Lum. dots, original hands,all in PRISTEEN condition.Additional [images].. 1966 Man-on-the-Moon Omega Speedmaster "Pre-Professional" Chrono and Bracelet in MINT condition! (Ref dmOGA10064) Ok, so in Figure 1 we have a pre-moon straight lug case (pre-1966) with a post c.861 (post-1968) dial... So either we have an early watch with a new dial, or a new movement and dial put into an old case. In either instance we have a put-together watch... Ok, so in Figure 2 we have a pre-pro dial (pre-1966) with a Pro (post-1965) case... So either we have an early watch with a new dial, or a new movement and dial put into an old case. In either instance we have a pur-together watch... Hey... maybe this watch (Figure 2) has the original dial for the other watch (Figure 1) and the first watch(Figure 1) has the dial for for this one (Figure 2)! A third instance was a personal one when I found what I thought to be the twin of my 1967 Speedmaster Pro at the Chicago Jeweler's mall. It looked identical, but in rougher shape. I mentioned it to David Greenspan to made a trip down to look at it, and it turned out to be a c.861 from 1968. Thus the only way to be really sure that there is a c.321 under the dial or behind the caseback is to take the back off (or ask for a picture of the movement if you are buying on-line. I hope this helps... -- Chuck