[Elecraft] K3 - REF CAL Question

[Lyle Johnson]

> You have to do that with your calculator :-)

C to F is fast and easy to do in your head.

The "real" formula is:

F = (1.8 * C) + 32

My mental algorithm is:

double the value,
subtract 10% (round it off, who cares if it is a degree or two off),
add 30,
then add 2 (if you feel the need for the extra precision).

Most of us can double a number in our head pretty easily.  Round it to 
the nearest 5 and then double it if you have trouble doubling 37 or 43 
or 51.  Hey! It's just the "two times" tables, which we all learned well 
before our 9th birthday.

Doubling and then taking off 10% of the result is the same as 
multiplying by 1.8 (or 9/5 if you prefer) but a heckuva lot easier.   I 
never did learn my "1.8 times" tables...

Again, round it if you trip over something like 74 - 7.4.  The answer is 
66.6.  But does it really matter if you decide to subtract 10 and get 
64?  Or subtract 7 and get 67?

Subtract 30 then 2 rather than 32.  Why?  Because it is easier to not 
deal with the 1's digit until you have to.  If you feel you have to.

I find that I can usually work it out in my head in under a second and 
get within a few degrees of the "correct" result.  Near enough for most 
needs.  If I'm tired it might take 2 or even 3 seconds to make the 
conversion, especially if I refuse to round things off (being an 
engineer, I sometimes get anal about numbers, which is a good indicator 
I'm tired!).

So, for example, let's take 52C. Is the PA too hot?

The real method:

2 x 52 = 104.
104 - 10.4 = 94 (near enough)
94 + 30 = 124
124 + 2 = 126(if you really care...)

If you'd rounded it:

   2 x 50 = 100
100 - 10 = 90
  90 + 30 = 120
120 +  2 = 122.

Still close enough to decide if your finals are cooking!  (They aren't). 
  Would the 4 degree difference have made you change you mind about the 
safety of your PA transistors?  I doubt it.

F to C is much slower, but I rarely have to do that :-)

Enjoy!

Lyle KK7P