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2nd October 2012, 06:51 AM  #21 
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Join Date: Aug 2010

More information.
My existing scale agrees with this. How to Read a Logarithmic Scale  wikiHow “Example: What is the value that lies halfway between the 10 and 100 decades on a logarithmic axis? Since it is the halfway point that is of interest, the quotient of steps 1 and 2 is 0.5. The nearest decade line with lower value is 10, so the halfway point's value is 10^0.5 × 10 = 31.62.” In my case my halfway point is about 1.3162 or about 1.32, see picture. 
2nd October 2012, 07:14 AM  #22 
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Join Date: Aug 2010

I added some ticks and numbers to the vertical axis so the chart can be be tested out. As before the ticks start with 1.2, the large line is 1.5. The horizontal line is a little busy to scale off of so in actual practice i might have to move the vertical scale a pixel or 2 up or down.
Hopefully someone that knows how to calculate the values by hand can compare the answers to the chart. 
2nd October 2012, 07:26 AM  #23 
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Join Date: Aug 2010

Here is a picture of a half way point as in 2 posts above from a commercial Dowell chart with tick marks including a mark for 1.1. Notice that it does NOT agree with the logarithmic scale. You should see 1.32 and instead see 1.44

2nd October 2012, 07:33 AM  #24 
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Join Date: Aug 2010

For comparison, here is the commercial chart complete. Notice how the decade tick marks do not look logarithmic at all. I do not know if the tick marks were fudged to fit the data or if there is more going on here than i am understanding.

2nd October 2012, 09:24 AM  #25 
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Join Date: Mar 2008

Powerbob,
looking at the other graphs you've posted, I'm inclined to think the tickmarks are garbage. your analysis looks right to me. can you please repost the modified plot of post #22, with tickmarks at the top as well? then I'll measure some values off the chart and compare them with the calculated results to confirm your tickmarking cheers, Terry 
2nd October 2012, 05:09 PM  #26 
diyAudio Member
Join Date: Aug 2010

Terry, If you mean reproduce all of the tick marks on the bottom horizontal line and place them on the top horizontal line that would be a huge job. It took me 12 hours yesterday to get as far as i did. Also my positional error is about the thickness of your green decade lines. If i tried to place lines at the top, my error could double. To place these lines i am measuring off of the green decade lines and making the ticks with Microsoft paint.
I did add more marks on the vertical axis though. But do not use the 9.5 position for this test, because i had to measure off the thick top line to place it. To get exact readings from the graph please use the shareware program “CrossHairs”. Mike Lin's Home Page Cross hairs is activated by a hot key and will position a cross hair across the screen to help read values on a chart, see post 18 for an example. CTRL tilde causes the cross hairs to follow the cursor, CTRL ! freezes the cross hairs, another CTRL ! removes the cross hairs. When you load in there are some set up options, i found the light pink lets me position the cross hairs the best, letting me see through them to the black tick marks. The program is a free download and fully functional. BTW, if you leave me 4 or 5 calculated positions around the chart using my tick marks for values i can see for myself how close i am. It may only be a matter of sliding the horizontal or vertical axis over a pixel or 2 to make things line up. 
2nd October 2012, 06:24 PM  #27 
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Join Date: Mar 2008

powerbob,
I cheated  printed it out, folded it in half and traced the marks. sloth is good. I hate to do this, but the marks arent right. here are some numbers: Phi = 1.2, p = 3.0 => Fr = 2.87 Phi = 1.3, p = 2.0 => Fr = 2.08 Phi = 1.3, p = 5.0 => Fr = 8.06 Phi = 1.4, p = 5.0 => Fr = 10.17 Phi = 1.5, p = 1.5 => Fr = 1.96 Phi = 1.5, p = 3.0 => Fr = 5.11 Phi = 1.6, p = 3.0 => Fr = 6.08 Phi = 1.6, p = 3.5 => Fr = 7.95 Phi = 1.7, p = 3.0 => Fr = 7.12 Phi = 1.8, p = 2.5 => Fr = 5.98 Phi = 1.9, p = 1.5 => Fr = 2.97 I picked (Phi,p) points with close to integer Fr values. HTH 
2nd October 2012, 06:55 PM  #28 
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Join Date: Aug 2010

Terry, These tick marks are way off. I may have to take your values and measure them and calculate position from them for the other decades. The only value i am missing is 1.1, can you please calculate that one also. As bonus can you calculate a Fr of 1.5 for a P of .5 and 1 and give me the exact Phi values.

2nd October 2012, 07:05 PM  #29 
diyAudio Member
Join Date: Mar 2008

Fr(1.5,0.5) = 1.03
Fr(1.5,0.5) = 1.38 Fr(1.1,2.5) = 1.93 Fr(1.1,4.5) = 4.08 
2nd October 2012, 09:12 PM  #30 
diyAudio Member
Join Date: Aug 2010

Terry, when you get a chance can you redo these two calculations.
Fr 1.5, P1, phi = should be around 1.6 Fr 1.5, P.5, phi = should be around 3.2 
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