On 19/11/2004 at 08:13 Andy wrote:

When it comes to calculations, the most useful ability is not to be able

to caculate it exactly, caculator or no, but to quickly be able to estimate a ball park answer or approximation.

Who needs to know that  22uH at 137kHz has 18.93 ohms reactance.

Its quicker to think  " a bit more than 20 times a bit less than 0.14,

times 6-and-a-bit

...    is  2.8 times 6-and-a-bit ,  so call it 18 ohms"

And they don't teach that in schools - and never have done, to my
knowledge!

Andy  G4JNT

I seem to recall a telecommunications professor (Ken Cattermole?) who expected 
his MSc students at least to have a feel for whether a result was of the right 
order of magnitude.

John G3PAI