Let's see who can answer this question first (without looking at a
thermometer!):
There is one point on the scale of a thermometer where the temp in Celsius
and Farenheit are equal. Which one?
Have fun,
Glenn ON4WIX
----- Original Message -----
From: "Joe Subich, W4TV" <[EMAIL PROTECTED]>
To: "'Lyle Johnson'" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
Cc: <[email protected]>; <[EMAIL PROTECTED]>
Sent: Wednesday, June 18, 2008 12:58 AM
Subject: RE: [Elecraft] K3 - REF CAL Question
F to C is much slower,
Not really ... (F - 30)/2 is generally within 10% and
(F - 32) * 1.1 / 2 is within about 1%. Both are easy/quick.
Unfortunately, mental math and estimation are skills that have
been lost with the "calculator generation."
73,
... Joe, W4TV
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Lyle Johnson
Sent: Tuesday, June 17, 2008 5:14 PM
To: [EMAIL PROTECTED]
Cc: [email protected]; [EMAIL PROTECTED]
Subject: Re: [Elecraft] K3 - REF CAL Question
> 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
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