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This discussion puts me in mind of why I joined ARSC a couple of years 
ago: Finding myself in a constant process of reinventing wheels, I 
thought that I might benefit from the experiences of others that had 
already gone down a similar path.  I was right. Thank you.

-- 
Charles Reinsch
KRAB Archive: www.krabarchive.com

On 10/26/2018 12:29 PM, Richard L. Hess wrote:
> Stuart,
>
> Your approach using area was counter-intuitive to me on the first 
> pass, so I decided to "check your work" and used my intuitive approach 
> which was to actually count turns (mathematically). The answer came 
> out the same.
>
> However, there is a minor error in your assumptions (not the formula). 
> It is a deep dark secret that North American tape thicknesses are the 
> base-film thickness, not the overall finished tape thickness (measured 
> in mils), while the Japanese and some European tapes have their 
> overall thickness listed in a nominal number of microns.
>
> Fortunately, Del Eilers and Bill Lund put together a wonderful 
> resource for 3M tapes, found here, and there is an equally wonderful 
> table in the same location provided by Friedrich Engel for BASF, AGFA, 
> and associated tapes. Alas, the Ampex tape list does not contain that 
> information.
>
> http://www.aes.org/aeshc/#AnalogTapes
>
> Here is a brief listing of overall tape thicknesses from 3M 
> categorized by "Play" Standard, Long, Double, and Triple. This should 
> work in a fixed pitch font. No tabs included.
>
>
>              Numeric Thickness Designations
> “Play"     nominal mil    micron     Japanese
> Standard       1.5         50.0         50
> Long           1.0         35.0         35
> Double         0.5         25.0         25
> Triple         0.5         18.0         18
>
>                  Actual Measurements
> "Play"        actual mil    micron     3M Type
> Standard       1.92        48.8         111
> Standard       1.93        49.0        201/2
> Standard       2.08        52.8         206
> Standard       2.06        52.3         250
> Long           1.27        32.3         150
> Long           1.43        36.3         203
> Long           1.51        38.4         207
> Double         0.85        21.6         200
> Triple         0.67        17.0         290
>
> Cheers,
>
> Richard
>
>
>
>
>
> On 2018-10-26 5:19 AM, ROBINSON Stuart wrote:
>> That assumption was stated in the original example.
>>
>> The tape thickness is a variable in the formula on the spreadsheet.
>>
>> Best, Stuart.
>> Archival AV Technician,
>> School of Scottish Studies Archives.
>>
>>
>>