What's so special about the watch?
As far as Seiko chronographs go, the 6138s have the bulk of the attention, both figuratively and literally. The larger dials and case sizes of the 6138s, while attention grabbing, lack the compact detailing that is present in their smaller compatriots like this guy here. This little guy here is presented in a the more uncommon case shape - slightly higher and more tonneau than the conventional Mini Jumbos. As far as collectability goes, I would rate this watch in a slightly better bracket than the usual MJs.
 
And despite the small size, the dial still contains much of the excellent detailing that makes it stand out even from the Jumbo from where it gets its namesake. To me all this adds up to give it a very military watch vibe, which I emphasized with the pairing of a green nato.
 
What are the functions of the watch?
30 minute chronograph, quickset day and date, time.
 
Let me tell you about the case...
Somewhat resembling a walnut, the case on this 6139 is a little thicker than the conventional mini jumbo. The mineral glass is flat across the raised case, made taller by a thin bezel that raises vertically from the stainless steel case. 
 
The case itself follows the profile of the bezel, cutting a slim figure as you look down at it on your wrist. The short horn lugs extend from the case, which has most probably benefited from a polish at least once in its lifetime. On the steel surfaces are signs of wear - small dings and scratches that are also apparent on the bezel. The caseback has not been spared the careless collector's (and hopefulyl not service person's) marks, scratches across the grab homes for the watch tool.  
 
And now the dial...
The matte black dial has a hint of a grey gradient in similar style to the blue dial. A sloping tachymeter rehault starts the decent into the centre of the layered dial, stark white digits printed onto a black ring. 
 
The next layer of the dial is a ring accentuated by hash markers of varying thickness - bold hours markers with orange lume dots at the ends accompanied by thin minute markers and a mico minutes to fill up the space. 
 
Moving inwards the dial is a clean black, the familiar silver Seiko brand applied at its 12. The rest of the markings on this part of the dial is printed in the same white as the tachymeter indicators - chronograph automatic in two lines beneath the applied logo, and the distinctive suma factory marking on top of the 30-minute indicator cut into the dial. 
 
A small detail that I like here are how the hour indices are cut diagonally where the sub dials intercept. Go zoom in and take a look. It's cool.
 
Cut into 3'O are the day and date windows, giving a three dimensional effect as the date window is deeper than the day one since it's been cut into the higher outer ring.
 
Let's not forget the hands...
Typical white 6139 hands are used in this case, the lume on this watch turning a sharp orange from age that is consistent with the lume dots at the end of the hour markers.