When you start Mathcad, you are in “automatic mode,” This means that Mathcad updates results in the worksheet window automatically. You can tell you’re in automatic mode because the word “Auto” appears in the message line, If you don’t want to wait for Mathcad to make computations as you edit, disable automatic mode by choosing Automatic Calculation from the Math menu or by

clicking the light bulb on the toolbar. The word “Auto” disappears from the message line and the checkmark beside Automatic Calculation disappears to indicate that automatic mode is now off.

Controlling calculations Automatic window update The word “Auto” on the message line indicates that you are in automatic mode. This

means that:

• As soon as you press the equals sign, Mathcad displays a result.

• As soon as you click outside of an equation having a “:=” or a “=, ” Mathcad performs all calculations necessary to make the assignment statement. When you process a definition in automatic mode by clicking outside the equation

• Mathcad evaluates the expression on the right side of the definition and assigns it to the name on the left.

• Mathcad then takes note of all other equations in the worksheet that are in any way affected by the definition you just made.

• Finally, Mathcad updates any of the affected equations that are currently visible in the worksheet window. Although the equation you altered may affect equations throughout your worksheet, Mathcad performs only those calculations necessary to insure that whatever you can see in the window is up-to-date. This optimization makes sure you don’t have to wait for Mathcad to evaluate expressions that are not visible. In automatic mode, if you print or move to the end of the worksheet, Mathcad automatically updates the whole worksheet. Whenever Mathcad needs time to complete computations, the mouse pointer changes its appearance and the word “WAIT” appears on the message line. This can occur when

you enter or calculate an equation, when you scroll, during printing, or when you enlarge a window to reveal additional equations. In all these cases, Mathcad evaluates pending calculations from earlier changes. As Mathcad evaluates an expression, it surrounds it with a green rectangle. This makes it easy to follow the progress of a calculation. To force Mathcad to recalculate all equations throughout the worksheet, choose Calculate Worksheet from the Math menu.

**Manual window update**

In manual mode, Mathcad does not compute equations or display results until you specifically request it to recalculate. This means that you don’t have to wait for Mathcad . to calculate as you enter equations or scroll around a worksheet. Mathcad keeps track of pending computations while you’re in manual mode. As soon as you make a change that requires computation, the word “Calc” appears on the message line, as shown in Figure 7-11. This is to remind you that the results you see in the window are not up-to-date and that you must recalculate them before you can be sure they are updated.

You can update the screen by choosing Calculate from the Math menu. Mathcad performs whatever computations are necessary to update all results visible in the worksheet window. When you move down to see more of the worksheet, the word “Calc” reappears on the message line to indicate that you must recalculate to see upto-

date results. xl Check results: a .xl 2 + b .xl + c = 0 a x22 + b x2 + C = 0 To process the whole worksheet, including those portions not visible in the worksheet window, choose Calculate Worksheet from the Math menu. To switch back to automatic mode, choose Automatic Calculation from the Math menu. Mathcad updates the entire worksheet and displays the word “auto” on the message line.

When you print a worksheet in manual calculation mode, the results on the printout are not necessarily up-to-date. When you’re in manual mode, make sure to choose Calculate Worksheet from the Math menu before you print. Figure 7-11: The word” Calc” on the message line indicates that recalculation is required. Interrupting calculations To interrupt a computation in progress:

• Press [Ese]. The dialog box shown below will appear.