How to Check a Calculator's Accuracy. Many people think that unless a calculator shows some gross abnormality, then it is performing correctly. Unfortunately, this is not true. A calculator can appear to be functioning normally and actually be erring its functions without its operator's knowledge. Yes, electronics can make mistakes! But, engineers have a simple test that will check for such errors, and they usually begin a work day by performing it. This test does not require the manipulation of complicated formulas. It uses a "magic number."

## Step 1.

The magic number is "370." Enter this magic number, 370, into your computer. Multiply it by 3. The computer total should show 1110.

## Step 2.

Enter 370 into your computer once again. Multiply it by 6. The computer total should show 2220.

## Step 3.

Enter 370 into your computer a third time. Multiply it by 9. The computer total should show 3330.

## Step 4.

Enter 370 into your computer a fourth time. Multiply it by 12. The computer total should show 4440.

## Step 5.

Realize that multiplying 370 by a number divisible by 3 will produce a total that has the multiple of three as its first 3 digits. For example, 27 is 9 threes If you multiply 370 by 9, the result is 9990.

Tip

The reason that this technique is an effective means of testing a calculator is that it runs through a sequence of computations that check for "slippage of digits." This is caused by a degradation of a computer's chips--something that can happen over time, particularly in the setting of outdoor elements in which engineers ply their trade.