Tentative attempt based on reviewing example programs in the documentation - descriptions used where no symbol is available.
: divide operation
, decimal point
Change Sign Presumably, changes sign of the contents of the central unit, ie. multiply contents by -1 and replace. Displayed as an elongated minus sign , when pressed?
C Clear central unit? What about other registers?
V (0-9) copy from 'central unit' to numbered register
V-inverted (0-9) copy from numbered register to central unit
+/- add/subtract number in central unit to/from value in add/subtract register.
* move content of +/- register to central unit, (sets +/- register to 0). Common calculator symbol for final result for addition/subtraction sequence?
Diamond copy content of +/- register to central unit; (keeps +/- register content). Standard calculator symbol for subtotals - aka Lozenge.
X/: copy number in central unit into X/: register with multiply/divide operation to be applied to the number that follows (is the expression evaluated on-the-fly or only when final = is entered?)
= copy number in central unit unto X/: register, complete the calculation and copy (move?) result back to the central unit (sets X/:- reg to 0?)
S add number in central unit to accumulator. (Performs an = operation first, subject to content of X/: register. See use here & schematic).
S variation of the above?
*S move accumulator content to central unit, similar to * symbol above?
Diamond_S copy accumulator content to central unit, similar to Diamond symbol above?
P (0-9) start definition of program in numbered program register
<number># input number to central unit
# print central unit content
J (0-9) jump to numbered program register
CJ (0-9) (conditional jump) - jump to numbered program register, if content of central unit is greater than or equal to 0. This simple command enabled 'true' programming.
A end program definition (stop learning)
(In addition, in the examples seen, registers are cleared before starting to run programs, with a sequence like this: * *S 1, = )
START1,START2 Deltronic-P - start program in program register 1 or 2
J (0-9) Combitron-S/Combitronic - to start executing numbered program register?
? stop a program
A entered by user after input of data, ie. like Enter key on standard keyboard.
P V_inverted (0-9) print the contents of numbered program register as a 14 or 15 digit number, referred to as a Zifferncode in the documentation. To make rekeying easier next time, if no paper tape available, or to allow for easier entry of printed programs such as ones published in brochures?
<Zifferncode> P V (0-9) no example seen, but perhaps the way to enter a program in a register as a Zifferncode?