Re: The DI Scale

Maynard Wright, P. E., W6PAP

Hi, Martin,

The fold is at 1 / (log(10)e).   Professor Maurice Hartung, in "how to use DUAL BASE LOG LOG SLIDE RULES," states that the fold is at 1/M where M = log10(e).  There are several uses for these scales, but since the LL scales on the N4 are unusual, and do not allow the determination of natural logs by using C and D, CF/m and DF/m are used for that purpose.  Common logs of numbers on LL are found on C and D with the N4.

The unusual relationship of the LL scales to the other scales on the N4 has some advantages.  It increases the range of the LL scales by increasing the high end to 10 ^ 10, much higher than the 20,000 high end of the Versalog.   The low end of the range is reduced to 10 ^ -10 as opposed to the approximately 0.0005 of the Versalog.  The Pickett LL scales consequently suffer a little loss in range on both sides of, and near, 1.0, but not much.

Since the N4 has both L and Ln scales, there are two ways each to find natural and common logs on that rule.

Best regards,


On 7/17/21 8:05 AM, Martin Potter wrote:
On Tue, Jul 13, 2021 at 08:37 AM, Maynard Wright wrote:
The CF/m and DF/m scales are folded at 2.30.
Is that 1/0.43429 or 1/(log(10)e) ?
Will have to add this to my list of "magic numbers".
... Martin

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