HP 35s HP 35s scientific calculator - User Guide - Page 114

If the equation is an assignment, only the right-hand side is evaluated. The result is returned to the X-register and stored in the left-hand variable, then the variable is viewed in the display. Essentially,  finds the value of the left-hand variable. If the equation is an equality or expression, the entire equation is evaluated - just as it is for . The result is returned to the X-register. Example: Evaluating an Equation with ENTER. Use the equation from the beginning of this chapter to find the volume of a 35-mm diameter pipe that's 20 meters long. Keys:  ( × as required)  Display       Description: Displays the desired equation. Starts evaluating the assignment equation so the value will be stored in V. Prompts for variables on the right-hand side of the equation. The current value for D is 2.5. Stores D, prompts for L, whose current value is 16. Stores L in millimeters; calculates V in cubic millimeters, stores the result in V, and displays V. Changes cubic millimelers to liters (but doesn't change V. Using XEQ for Evaluation If an equation is displayed in the equation list, you can press  to evaluate the equation. The entire equation is evaluated, regardless of the type of equation. The result is returned to the X-register. 6-12 Entering and Evaluating Equations