number stored in memory location 312 called 34 z 34 x y and z with their associated labels are treated as a stack memory location 313 called 34 t 34 and memory location 323 called 34 tlabel 34 are the top of the stack and are not displayed x y z and t and their associated labels may contain the nothing fig2 c is a flowchart of a program for adding and deleting entries from the stack additional details about the stack performance is evident from the discussion below memory location 314 and memory location 324 are also permanently assigned memory locations memory location 314 contains the null set or a 20 bit address of alphanumeric string which is used as a current equation as explained below memory location 324 contains the null set or a twenty bit address of a memory location containing the parsed version of the alphanumeric string pointed to by memory location 314 as explained below fig2 a is a block diagram of a program implementing an equation solving interface the program can be in an entry mode 202 or a calculating mode 203 in entry mode 202 plurality of keys 103 and 104 can be used to enter a equation into calculating device 100 the equation is entered as an alphanumeric string pointed to by memory location 314 more discussion on exactly how to enter an equation and how an equation is displayed by display 111 is found below once an equation has been entered into calculating device 100 a user may enter into calculation mode the actual steps necessary for a user to perform are discussed more fully below calculating device 100 parses the equation displayed by display 111 in order to extract mathematical variables and to determine the mathematical relationship between.