Return-Path: Received: (qmail 2931 invoked from network); 19 Nov 2004 15:15:06 -0000 Received: from unknown (HELO ptb-spamcore02.plus.net) (192.168.71.3) by ptb-mailstore01.plus.net with SMTP; 19 Nov 2004 15:15:06 -0000 Received: from mailnull by ptb-spamcore02.plus.net with spamcore-l-b (Exim 4.32; FreeBSD) id 1CVAT6-0002wD-Q5 for dave@picks.force9.co.uk; Fri, 19 Nov 2004 15:14:37 +0000 Received: from [192.168.67.1] (helo=ptb-mxcore01.plus.net) by ptb-spamcore02.plus.net with esmtp (Exim 4.32; FreeBSD) id 1CVAT6-0002wA-Jj for dave@picks.force9.co.uk; Fri, 19 Nov 2004 15:14:36 +0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore01.plus.net with esmtp (Exim 4.30; FreeBSD) id 1CVATZ-000HsX-1w for dave@picks.force9.co.uk; Fri, 19 Nov 2004 15:15:05 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1CVASR-0004Cm-Im for rs_out_1@blacksheep.org; Fri, 19 Nov 2004 15:13:55 +0000 Received: from [193.82.116.30] (helo=relay.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1CVASR-0004Cd-7t for rsgb_lf_group@blacksheep.org; Fri, 19 Nov 2004 15:13:55 +0000 Received: from smarthost0.mail.uk.easynet.net ([212.135.6.10]) by relay.thorcom.net with esmtp (Exim 4.41) id 1CVASK-0008Q8-Qh for rsgb_lf_group@blacksheep.org; Fri, 19 Nov 2004 15:13:55 +0000 Received: from tnt-2-115.easynet.co.uk ([195.40.196.115] helo=erica) by smarthost0.mail.uk.easynet.net with smtp (Exim 4.10) id 1CVASJ-0002ug-00 for rsgb_lf_group@blacksheep.org; Fri, 19 Nov 2004 15:13:48 +0000 Message-ID: <000401c4ce4b$08ef8340$73c428c3@erica> From: "g3ldo" To: rsgb_lf_group@blacksheep.org References: <01C4CE0F.A626D2D0.actalbot@southsurf.com> Date: Fri, 19 Nov 2004 10:36:05 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.50.4522.1200 X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4522.1200 X-SPF-Result: relay.thorcom.net: 212.135.6.10 is neither permitted nor denied by domain of ukonline.co.uk X-Spam-Score: 0.8 (/) X-Spam-Report: autolearn=no,DATE_IN_PAST_03_06=0.68,RCVD_IN_SORBS=0.1 Subject: LF: Re: calculations Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Status: No, hits=0.7 required=5.0 tests=DATE_IN_PAST_03_06 autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-Spam-Filtered: by PlusNet SpamCORE (v3.00) > 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" > > Andy G4JNT > I agree with Andy. Part of my degree course with the Open University was a unit called Modelling with Mathematics. At the time (mid 1970s) we were provided with circular slide rules, which were adequate for determining whether something would work or not. At the time electronic calculators had become available and many students complained about having to use the slide rule. The course team responded by saying that the slide rule gave a better understanding of the mathematics involved. Peter, G3LDO