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Abstract
A critical examination of the original Ångström pyrheliometric scale has been made from the result of recent calibration of the new modified Ångström pyrheliometer using the sun as radiation source.
The mean marginal error of the old standard pyrheliometer is found to be + 2.4 per cent. The influence of the small difference in aperture of the two models is esteemed to increase the correction insignificantly.
This result is equivalent in meaning that the original scale-values added with 2.4 per cent are given in the true energy scale.
The corrected values are nearly one per cent higher than in the pyrheliometric scale recommended by the Radiation Conference at Davos 1956.
A practical pyrheliometric standard scale is a question of specification of the aperture conditions or of the amount of circumsolar sky radiation to be allowed in the standard pyrheliometer. A proposal of such a specification is given and recommended by the Conference at Davos.