Make full use of your scientific calculator in the exam

CPL Assist
When you prepare yourself for studying for the Comm. pilot exams, a scientific calculator should be high priority; not because you are going to become a mathematician over-night, but because, apart from the plus and minus keys, it has some really useful time saving keys.

As you will discover, you will, one minute, be working with ridiculously big numbers (SHF weather radar has a typical frequency of 9, 375, 000, 000.00 cycles per sec.), and the next, very small numbers (a pulse of radar might be 0.000, 003 seconds in duration). Just the number of zeros, when typed into a calculator wrongly can cause your calculation results to be out by 10 or 100 times the value.

So how does the scientific calculator help with finger trouble?

Well, it has a really smart little key with the letters; EXP printed on it. This is not, as some hope; extra sensory perception, but rather; ‘exponent or exponential’. It does that mathematical thing of multiplying your input number times ten raised to the power of a second number. You don’t have to worry too much about that because in more simple terms, it moves the decimal place by a specified number of positions. Even this might be too much to think about for the non maths-boffin, so lets look, rather, at how and where to use it.

Frequencies are always large numbers. A radio signal only starts to propagate at 15, 000 Hz. To over come the use of large numbers, radio people talk in terms of Kilo Hz (1000Hz), Mega Hz (1,000,000Hz) and Giga Hz (1,000,000,000), so 1 Mega Hz is one million cycles per second. Now, how do we put 1 Mega Hz into a calculator? We simply type 1 and use the EXP key to move the decimal place 6 places to the right. Typing EXP 6 does that.

So if 1 MHz is typed: 1 EXP 6, how do we do 1 KHz (Kilo Hz). Kilo is thousand, which is 3 zeros and is typed: 1 EXP 3.

Following on from that, 1 GHz (one thousand million), which would be 1 followed by 9 zeros, is typed 1 EXP 9.

It’s as simple as that. If there are fractions of these values, you don’t change the technique:

37.256 MHz is typed: 37.256 EXP 6

2.3 GHz is typed: 2.3 EXP 9 Etc.

For radar, where the numbers are small, you can also use EXP, but this time with minus values. In radar you work with microseconds, which are millionths of a second. To enter these into the calculator, you use EXP –6, because you want to move the decimal place to the left. Be careful because on some calculators you can type the –6 directly and on others you must use EXP 6 +/- (plus-stroke-minus is printed on the key for change sign).

Typically you would be given a pulse recurrence period of 1500 microseconds. To put this into the calculator, type: 1500 EXP –6 – it’s as simple as that.