Thsnks. I will email you presently.
After writing that first post, I also managed to stumble across the Hakuto Denko HA-151B. It looks like an almost identical unit to the PGS-151, and it is currently available, so I've contacted them for more info. A manual for that one is available here...
Title says it all. I came across a handleful of these and am looking for info about them. I can't find any info about the manufacturer, they don't seem to have an internet presence. Thanks in advance