A widely used technique for controlling scale deposition in desalination practice is by dosage of anti-scalants. Fundamental techniques for assessing the relative effectiveness of different anti-scalants are of considerable interest The objective of the present research was to extend a technique characterizing the effectiveness of anti-scalants by identifying the threshold concentration at which scale deposition is unaffected by transport hydrodynamics and is purely surface controlled. A lower threshold level denotes higher inhibition effectiveness. The system investigated consisted of an electrically heated annular flow heat exchanger enabling measurement of calcium sulfate scale deposition on a stainless steel heating surface at a constant surface temperature. Application of the technique is illustrated by scale deposition measurements performed at varying Reynolds numbers in the absence and presence of three anti-scalants and at different scale deposition temperatures. (C) 2016 Elsevier B.V. All rights reserved.