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.
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
"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
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.
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada 647 479 2800
Quality tape transfers -- even from hard-to-play tapes.