Gack.
Sorry to flood people's in-boxes, but I've just realised two inaccuracies of measurement terminology in the below.
Where I wrote 'these are rounded up to the nearest hundreth of an inch' in the second paragraph, I obviously meant 'these are rounded up to the nearest thousandth of an inch'.
Where I wrote 'Given the consistent relationship between quarter inches and .4 of a millimetres' in the second sentence after the Binford formula, I obviously meant 'given the consistent relationship between 64ths of an inch and .4 of a millimetre'.
Sorry for any confusion caused. If I've made any other mistakes, please do feel free to let me know.
Alasdair
----- Original Message -----
Subject: Re: clay pipe stems in metric
From: "Alasdair Brooks" >;[log in to unmask]>
Date: Thu, October 25, 2007 12:22
Following up from my own post (and apologies if anyone's answered in the interim - I only subscribe to the digest version, so don't always see every reply immediately), I think I can quantify the precise problem...
Here are the traditional stem bore hole measurements and dates, with the nearest metric equivalent rounded up to the nearest tenth of a millimetre. Decimal inch figures are also provided after fractions; these are rounded up to the nearest hundreth of an inch.
1590-1620: 9/64" (.141") = 3.6mm
1620-1650: 8/64" (.125") = 3.2mm
1650-1680: 7/64" (.109") = 2.8mm
1680-1720: 6/64" (.094") = 2.4mm
1720-1750: 5/64" (.078") = 2.0mm
1750-1800: 4/64" (.062") = 1.6mm
Now here are some typical metric drill bit sizes, converted to decimal inches:
.5mm = .019"
1mm = .039"
1.5mm = .059"
2mm = .078"
2.5mm = 0.98"
3mm = .118"
3.5mm = .138"
Quarter inch increment drill bits and half a millimetre increment drill bits therefore don't correlate precisely (except where 5/64" is essentially equal to 2mm). I can see ways of addressing this mathematically given that a quarter inch is essentially equal to .4mm, but this is complicated by the lack of consistency in dating periods, which vary between 30-50 years. I think I can make the necessary adjustments for a metric conversion, but if someone's already done it, I'd be grateful for being given an excuse to be lazy and spare myself the work.
Now, this leads us to Binford's:
Y = 1931.85 - 38.26X
Does anyone have an opinion on whether we might reliably turn '38.26' into 'the number of years between each .4 of a millimetre decrease' and 'X' into the 'mean millimetre hole diameter for the group'.
Given the consistent relationship between quarter inches and .4 of a millimetres, as noted above, I can't see a problem with re-imagining the regression formula as a straight metric conversion, but again, I'd welcome any thoughts people might have on the issue.
Note that I'm not trying to engage here with discussions on the reliability of clay pipe dating generally or Binford's formula specifically, merely trying to convert to metric for educational & training purposes.
If anyone wants to contact me off-list, please use: [log in to unmask] - but I'd welcome on-list discussion as well.
Thanks,
Alasdair Brooks
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