If you're having trouble using a calculator, the best advice is to read the manufacturer's instructions.

Different calculators operate in different ways, and they don't always follow the same order for entering numbers and functions.

Here's a few general hints on how to use a calculator effectively.

1. Clear the calculator before you start any new calculation.

This will ensure that nothing you did before gets mixed up with the calculation you are about to begin

2. Write down the numbers first if they are complicated.

You should also write them down if someone is calling them out to you, such as while taking a series of measurements.

Then you can be sure that you're entering the right numbers, especially if they have decimal points or several zeros.

3. Estimate the answer in your head if the numbers are long or complicated.

This will help you to pick up mistakes, because it will give you an idea of the size of the answer you're looking for.

For example, if you had 18 rods that were each 4.2 metres long, and you wanted to know what the total metreage was, you could do the following calculation in your head:

     20 (rounding up 18) x 4 (rounding down 4.2) = 80

So when you do the actual calculation and find that the answer is 75.6 metres, you'll know that it sounds about right.

The rule of thumb for rounding off numbers is:

     Ending in a 5 or more - round up

     Ending in a 4 or less - round down