Relascope for measuring the basal area (m2) of a stand of trees.
This is a relascope/angle-gauge, intended for gathering data when calculating the standing basal area (m2) of a timber crop. Made using a plug chain and key ring to set the distance of the sight from the user, by placing the ring to the cheek bone below the observing eye and extending the arm holding the sight to the full extent of the chain, when making the 360° sweep sighting of the number of stems of the crop at the Breast Height Diameter (BHD) of 1.3m up the stem. It enables the measurement of the approximate basal area (m2) of the crop, without having to lay out plots of a known diameter, before measuring individual trees BHD to calculate the stands basal area (m2).
This particular instrument has a chain length of 50cm and an internal cross piece width of 1cm giving it a ratio of 1:50.0 and a Basal area factor of 1.
Glass prism relascopes were also manufactured, but owing to the material they were made from, often ended up in two or more pieces in the users pocket!
A full description of relascope calibration and use, along with formulae, can be found in the FC publication, ‘Forest Mensuration’. A handbook for practitioners. Robert W Matthews and Ewan D Mackie 2006. ISBN: 978 0 85538 621 4
Additional images of this relascope are attached as a pdf.
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