> 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 > > _______________________________________________ > Elecraft mailing list > Post to: [email protected] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
