That box is a dinosaur today.  It is the first yield monitor C-IH put out.  It worked very well and was very accurate.   As Torn said, it uses SRAM cards and Windows  98 is the only operating system that will consistently read them.  I think I was able to read them in Win 2000 (after jumping through a lot of hoops) but I don't remember every getting Windows XP to read them.

I am not sure on this, but I think an AgLeader PF3000 could be dropped in place of the black box monitor using the same cables.  Someone will correct me if I am wrong.  The 3000 is discontinued, but it uses flash cards.  They are much easier to read.  I am sure there are still some PF3000's around that could be had very cheap.  I still have several of the flash cards around.