Author presents log-log eq (6) as the constant-elasticity form 'used by most demand analysts', with a printed coefficient and SE for own price; he judges (5) and (6) 'equally reasonable' with 'very little to choose' between them, so the -0.8928 log-log coefficient is the headline own-price elasticity || 'The logarithmic equation (4) is of the type used by most demand analysts, chiefly because it produces constant elasticities.' ... 'These values are close to those occurring in (6) and therefore equally reasonable.' (p.366-367)
Houthakker, H. S. (1951): “Some Calculations of Electricity Consumption in Great Britain.” Journal of the Royal Statistical Society: Series A 114(3), 351-371