[dlafbjwa] 5 choose 2 digits

Binomial(5,2)=10, so we imagine various ways of encoding digits this way.

Maybe 2 lit dots in a collection of 5: In a 7-segment display, or actually any depiction of Arabic numerals, we can guess at what the digit is by the total amount of light emitted; perhaps an eavesdropper only sees a "reflection" of the digit on a matte surface.  In contrast, if there are always exactly 2 (out of 5) segments illuminated, and all segments are the same size, then the light output will remain constant no matter what digit is displayed.

Type a digit by pressing 2 buttons out of 5.  We do have 5 fingers.

Edges of a 4-simplex.