This is a thoroughly-commented piece of ASSEMBLY code.

mult_two.asm

; THIS PROGRAM MULTIPLIES A NUMBER BY 2
; Made by Jose Salvatierra
; For a further explanation go to 
START:      LDN NUM1    ; Copy variable negated into the accumulator (this is the value we are working with in the processor)
            SUB NUM1    ; Subtract from the value in the accumulator the value of NUM1 (this is essentially multiplying by 2)
            STO MYSUM   ; Store to variable (copy the value we're working with to the variable MYSUM)
            LDN MYSUM   ; Get the value of the variable multiplied by -1 (negated) into the accumulator
            STO MYSUM   ; Store to variable (copy the value we're working with to the variable MYSUM)
            STP         ; Stop the processor (ends the program)
NUM1:       VAR 750     ; Declare 32-bit variable with value 750
MYSUM:      VAR 0       ; Declare 32-bit variable with value 0