Rare Brietling Navitimer chronograph MK5 Ref 806, Venus 178, from 1966, pilot watch.
 
The Navitimer was introduced in 1954 and aside from some very rare early Valjoux 72 models, the piece was normally equipped with the equally excellent 17-jewel Venus 178 until the 806 rode off into the sunset in 1972-1973. 
 
The case, movement and dial are correct for a 1966 MK5. 
The sliderule is a service replacement correct for 1968 and later.
The main hands are NOS replacements which are correct.
The Sub Second dial hands are from the MK8 "Big Eyes" from 1968 and later. These are there not correct for the reference and year.
Please see the images as these compliment and aid the description provided below.
 
Dial:
The dial is in good, original condition. There is no wear to writing. There is some marking at 4 o'clock, on the edge of the dial, in a dark brown colour. 
Hands:
The hands are correct, NOS replacements.
 
Glass:
The plexi-glass is in near perfect condition, with only some very light surface scratches. This is a replacement.
 
Crown:
The crown is original, signed with the Breitling logo.
 
Case:
The case is in good condition overall, with the lugs in a good condition, with sharp edges, free of serious nicks and dents. The side on 9 o'clock has some nicks to the case, all visible in images.
 
Case back:
Strong condition with light surface scratches. The original light grained finish remains well. There are some deeper marks, as seen in the images, which relate to poor opening of the case back in the past.
 
Strap:
The strap is a genuine Breitling Blue Leather strap with a Breitling raised logo polished buckle, with the strap marked "Brietling, Manufacture en Suisse, 22-20, 314X. The strap is in worn, but good condition.
 
Movement:
Keeping time to within -25 seconds a day with an amplitude of 270 degrees. The beat error is 0.2m/s. This is a movement in good health.
 
Case dimensions:
Case width: 41mm
Case width with crown: 43.7mm
Case length: 41mm
End of lug to end of lug: 48mm
Case Depth: 12.5mm
Lug width: 22mm