You silly! Now we're really bass ackwards! No really, I just refer to this issue as Er (Relative Permativity or Effective Dielectric Constant). The variance(s) found are many. I believe that some of this "tweaking" to get the formulae to work may be due to the original Motorola MECL algorythms that were written back in time when big hugh (wide) traces were abundant and fast/clean PTFE samples were supplied for test vehicles. (Or something like that) The success is all in not repeating the same mistake twice. <Take thorough notes/libraries/archives> TTYL Groovy ______________________________ Reply Separator _________________________________ Subject: Re: Controlled Impedance Author: [log in to unmask] at SMTPLINK-HADCO Date: 5/21/96 4:59 PM Subject: Time: 1:14 PM OFFICE MEMO RE>Controlled Impedance Date: 5/21/96 If "dielectric constant" weren't a constant, we'd call it a variable wouldn't we? (;-) So let's propose a new term "dielectric variable" -- or should that be "variable dielectric". That might be better yet, then we could adjust the dielectric to fit our needs by stimulating the dielectric with frequency, temperature, humidity, pressure, voltage, material ratios, etc. Ralph