Quirky Old Technology

I'm sure most people who at into technology and gadgets have a whole heap of old stuff lurking around in the back of cupboards, in lofts or garages. Well here is one of mine, still with box:

Yes, a Casio PB-100

Pop in a couple of CR-2032 batteries and it still works, albeit with a very faint screen

So I fired it up and entered in the first program in the manual (yes, still in the box)

10 INPUT "N= ", N
20 S=0
30 FOR I=1 TO N
40 S=S+1
50 NEXT I
60 PRINT S
70 GOTO 10

Lovely BASIC nostalgia feeling aside, this doesn't really do much but when I ran it I got some very strange behaviour:

ERR6 P0-20

(Incidentally, Change to MODE 0 and SHIFT 0 to run)

P0 is the program in slot 0 and -20 is line 20. Now, line 20 is the rather innocuous assignment of S=0 and ERR6 from the separate technical manual is :

Variable error

• Attempt was made to use the same memory for a numerical variable and a character variable at the same time
• Do not use the same memory for a numerical variable and a character variable at the same time

This is interesting, a character variable is assigned with a $, for example A$. So the assignment S=0 should be fine.

Then If I change to from S to P, say, it all works fine and then changing back to S it worked again. Very mysterious.

Yes, I did make sure I didn't enter S=O !

So no real idea what's happening, probably some path in the internal circuitry is failing but at least I managed to get it working in the end.