Here we have a 1988 Precista PRS-17 ‘Big Triangle’ UK Royal Navy Issue Diver, reference 6645-99-75733 14. It has a 39mm Stainless Steel case, with uni-directional countdown bezel, having the original black and silver insert with lume pip. It has a screwdown crown to the right-hand side. It has the black dial with ‘big triangle’ at 12 O’clock. It has the Arabic explorer layout with the military Tritium marking. To the rear is the screw back with the NATO reference, broad arrow and serial number 1664/88. Inside is the original ETA 955.114 Quartz movement.
 
The Precista brand originates from the English watch and clock material supplier, Southern Watch & Clock Supplies Ltd. The CWC and later Precista diver watches issued to the Royal Navy during the 1980s were the successors to the Rolex Military Submariner.
 
The NATO reference of 6645-99-757-3314 and serial number 1664/88 are to the reverse of the case back, following the normal issue format.
 
The Precista issued diver watches were produced in relatively small quantities over 1988 and 1989, making the watches attractive to collectors.
 
An all-original example. The mineral crystal glass has been left in original condition with marking. 
 
Full condition report below. Please see the images as these compliment and aid the description provided below.
 
Dial: 
The dial is original and is in very good condition. It has a black matte finish with White signing which is good and unworn. There is no visible marking. The Tritium lume is original. 
 
Hands: 
The hands are original and are of Plongeur style. They are in good condition in a white tone. They have the original lume in-fill.
 
Glass: 
The mineral crystal is original and has noticeable marking. 
 
Crown: 
The crown is original, formed of steel. It screws down as it should. It has some light marks.
 
Case:
The case is stainless steel and is in good condition. It has a brushed satin finish. 
 
Caseback:
The case back is Stainless Steel and is in good condition with brushed finish and clear engraving. It has some small light scratches. 
 
Strap:
The watch comes on a new Zulu Diver elastic NATO strap.
 
Movement:
The movement is an ETA 955.114 quartz calibre. It has a jewel count of 7, with hours, minutes and central seconds.
 
The service history is unknown. The movement is in good condition and has had a new battery fitted. It is keeping accurate time.
 
Case dimensions:
Case width: 39mm
Case width with crown: 42.5mm 
Case length: 38mm 
Case length lug to lug: 44.25mm
Case Depth: 11mm
Lug width: 20mm