Ofmega Mistral (10th style) black derailleur

The Ofmega Mistral has its enthusiastic fans - who claim it is made of a ‘hi-tech polymer’ - not ‘plastic’ (like a despised Simplex). It is a genuine, high quality, precision, cycling product, not merely one of Darth Vader’s minor internal organs.

And now for the nerdy stuff... Despite being manufactured in modest numbers, the Mistral was produced in a bewildering array of different versions. And just to make it perfect, information about them is very hard to get clear:

There are seven different colours, black, grey, blue, pink, yellow, white and green. The first two colours are generic, the blue is the signature colour of Italian national teams and the the final four colours mirror many of the trophy jerseys in the Giro D'Italia and Tour de France.
There are two different lengths of parallelogram arms, long (52mm) and short (42mm). I believe the long arms were only on early models (around 1982-3), although I think that the availablity of long and short arms may have overlapped.
There are two different b-knuckles. The initial b-knuckles have a simple triangular b-pivot stop. Very late in the Mistral's life (around 1987?) the b-pivot stop acquired a couple of reinforcing buttresses. This, very late, b-knuckle is similar to that used on early versions fo the Ofmega Mundial.
There are three different types of outer cable stop. I believe that the earliest versions (1982-3?) have a round knurled adjuster, slightly later (1983-5?) versions have a hexagonal adjuster and the final versions (1986-7?) have no adjuster at all. The 'no adjuster' component is shared with the Ofmega Mundial.
The b-pivot Allen bolts and p-pivot spring covers are steel in some models and aluminium in other models. I don't know if this tells you anything about the date of manufacture.
On some models the p-pivot Allen bolt is a black 6mm item, on others it is chrome and 6mm, on others it is black and 5mm and on yet others it is chrome and 5mm. I believe that the early models (with a cable adjuster) had 6mm Allen bolts and later models (with a fixed cable stop) had 5mm Allen bolts. But I don't know if the colour of the bolt tells you anything about the date.
Most Mistral's have pulley wheels with very short 'teeth'. Very late Mistral's have pulley wheels with distinctly longer 'teeth'. There are also an astounding array of different pulley wheel dustcovers, which could be painted creamy white or polished metal or brushed metal. The painted white and brushed metal versions tend to be on early models and the polished ones tend to be on late models.
Most Mistrals have an inner pulley cage plate that is nicely made with rounded corners and a brushed metal finish. On very late Mistrals this plate is more crudely stamped out and is vaguely polished.

There are a couple of oddities about this story that swim against the tide of history:

Longer parallelogram arms are usually associated with derailleurs that have more sideways movement - and so can cover a sprocket cluster with more sprockets. As bikes inevitably get more and more gears, the trend of history is therefore for parallelogram arms to get longer, not shorter. So why did Ofmega move from longer arms to shorter arms?
During the 1980s the big news was the arrival of Shimano's SIS indexed derailleurs. Cable tension was central to this system (and still is). So the trend of history was for derailleurs to acquire cable adjusters. So why did Ofmega ditch its cable adjusters?

Confused? You certainly ought to be!

This, exquisitely preserved, Mistral has the following attributes:

It is black. The black Mistral was less glamourous than the other colours - but it was the colour that retained its youthful looks even after being pelted with corrosive oily slime - and it sold surprisingly well.
It has short (42mm) parallelogram arms (note the small space between the adjustment screws).
The b-knuckle has 'buttresses' on the b-pivot stop.
It has a fixed cable stop.
The b-pivot Allen bolts and p-pivot spring covers are steel.
The p-pivot bolt takes a 5mm Allen key and is chromed.
The pulley wheels have long teeth and polished dust covers.
The inner pulley cage plate is crudely stamped and vaguely polished.

I think that these features make it a very late Mistral, perhaps from around 1987. It weighs a, relatively beefy, 192g.