Pentax made the meter, but Honeywell was their official importer, so in the USA, their products meters were cobranded at the time.

The name comes from its performance: it measures a 3° area inside 21° field of view. Like the SEI Photometer, it's telescopic, but the SEI uses an internal light bulb to compare against the surrounding field; this Pentax measures the reflected light of that little spot.

This is one of the earliest of the new wave of CdS meters that took over the market in the early 1960s, along with the Gossen Lunasix and Sekonic's Microlite. Those three meters also showed the world of the metering future, at least until digital took over. The Microlite was the simple one, the Lunasix was the professional "system" meter with various attachments, and this was the affordable spot meter.

This is the earliest version, which looks upside down. You hold the box in the palm of your and and look down on that black stove-pipe. There's a 45° beamsplitting mirror inside, and you get part of the light and the meter gets the rest. Later versions would be further restricted to a 1° area, and changed to a more comfortable pistol-grip design.

One of the oddest things about this is that takes two different batteries: the standard 1.35v mercury battery that you can no longer find, and a 22.5v Eveready 412 which, strangely enough, is still available.

This is still quite a nice machine, if you can get the batteries sorted out. The little button battery runs the high-light-level system, since you don't really need much juice for that. The big one kicks in for the low-light circuit. The lens on the front is a 100mm f/2.5, which gathers a lot of light, and the meter scale is big and easy to see. I wear glasses and some of these eyepiece designs don't work very well, but this one is a joy. The calculator scales on the lens make sense—you don't really need to read the instructions to figure it out. The front lens is threaded for 46mm filters so you can measure directly through the filter. And there are lugs on the side for a neck or hand strap if you're so inclined. It's also suprisingly light, considering it's size.

Got mine the way I acquire most of my high-end stuff: broken. Sometimes I'm actually thankful that people let their batteries leak and ruin the battery chambers of cameras and accessories; I get a lot of bargain equipment that way.

This meter bears a strong familial resemblance to my Mekano Spotron Pro. I don't know if they were truly made by the same people, but I believe so.

There's an interesting webpage about this meter at Dave Schneller Photography.