Grid Explanation

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Explanation of 1989 Gridding of T-26

Staff members Jon Berkin, Mathew Wilcox, Liz Cahn, and Nathan Meyer adopted method suggested by Erik Nielsen of triangulation from 4 column bases to establish picchetti for area to be excavated in 1989.

Method used was to measure the distance from said column bases to SE corners of meters as detailed on 1987 site plan.  These measurement were then scaled up to actual dimensions on site.  4 long tapes were used to establish point where these measurements joined.

We decided to establish 4 picchetti in a 5 square meter area.  Choosing the picchetto which had had the closest fit with its 4 separate measuremetns, we then adjusted

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the relative positions of the other three.  The picchetti thus established for T-26, and the measurements used to located them are as follows:

Example drawing of measurements

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This system is the best that can be accomplished without either of the 1988 site plans, access to fixed points and a transit.  Difficulties leading to imprecision were encountered in the following points:

1. 1987 site plan made available was on velum, which had shrank, making absolute correlations of site plan scale to actual site scale imprecise.
2. Hanging 4 long tapes introduces the variability of wind and bows in the tapes.
3. Conditioned on the above two factors, the 4 tapes did not always meet exactly but formed a \'hat\' in which we had to suspend the plumb bob and place the picchetti.

Note: Reevaluation of this work shows that the grids from which I triagulated were denoted on a master plan which numbers the meters along the southern wall of the upper building as starting at 1 not 0.     Nathan Meyer July 11, 1991