I have a 1246S with a special feature (please see photos).

I believe it is to increase the memory.

Someone could help me how to use?

Photo 1

Photo 2

Photo 3

I tend to think it's a speedup switch rather than a memory switch.

OT: I once had one of those 1246S. The rubber coated keyboard is awful, the contact domes under the rubber were very unreliable...

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I tend to think it's a speedup switch rather than a memory switch.

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It's hard to tell from the third photo, but there could be a second RAM chip soldered on top of the other with the red switch selecting one of the two.

The way to find out would be to enter a short program, set the switch to the other position and see, if it's still there. And vice-versa.

Does not increase the speed I've tested (Calculator Speed Benchmark using the N-Queens Problem)

Max, it may likewise be a higher capacity RAM but the effects of the switch are probably the ones you suppose.

I've tried and nothing has changed (program)

Possibly with double the memory, and the switch selects between two banks?

Memory (MEM) reports 7,422 bytes in any position

I think I've found the switch function.

There are two banks of variables (a. .. z).

They are preserved function equal to P <> S HP-67

That's basically what I said. I think you'll find that it's not just the variables.