It is at this stage that any adjustments resulting from the sulphur dioxide examinations are applied to the basic thickness. Manufacturers must then guarantee that no slate is thinner than this value. Considering slates are sold on the basis of nominal thickness; in case the range difference is large the moderate thickness will be a great deal larger than the minimum. If variation is small then they will become much nearer. This procedure ensures your slates are technically satisfactory but there is a different route in which it is important for conservation reasons to make use of thicker slates. These may be specified on the basis of traditional construction methods. Obviously it can be unwise to use this alternative to indicate thinner slates than required to resist the weather stress.