The word "substantially" is frequently used in claims and is permissible provided it conveys the necessary meaning (Leonardis v Sartas [1996] 449 FCA 1). "Substantially" merely indicates an intention that the term it qualifies should not be read too literally. As explained by Blanco White, Fifth Edition, at 2-112:

"If draftsmen and judges were perfect 'substantially' would have no effect; as it is, the indication is often a useful one. But the word can only mean 'nearly enough for the patentee's purposes', unhelpfully unless the body of the specification tells the reader what those purposes are and what sort of precision is needed to achieve them."

"About"

Similarly, the word “about” is often used to qualify (in particular) numerical quantities to indicate that small variations from the specified value are envisaged. In general, all terms used in a claim permit a degree of variation consistent with what a person skilled in the art would understand from the specification. In Catnic Components Ltd v Hill and Smith Ltd (1982) RPC 183, the term 'extending vertically' was construed in context as meaning 'near enough to vertical to enable ...'. However, numeric values invite a construction limited to the precise value. The use of the word ‘about’ to qualify a number is merely an express indication that the number is not to be construed as a precise value.

When ‘about’ is used to indicate a variance, the extent of that variance is dependant upon what the person skilled in the art would understand is intended. In this regard, the precision of the quantity would also have a bearing. For example, “about 10” might permit a variance of several units, however “about 10.301” would only permit a variance of a small fraction of a unit.

The use of ‘about’ to qualify the extent of a range, e.g. ‘about 10 to about 20’ (or the equivalent phrase ‘about 10 to 20’) does not in itself render the scope of the claim uncertain. The extent of variation encompassed by ‘about’ is likely to be primarily dependant upon the size of the range (in addition to numerical precision). For example, a range of ‘about 10 to about 1000’ would reasonable permit variance of many units at either end of the range. However, a range of ‘about 10 to about 12’ would likely only reasonably permit a variance of a fraction of a unit at either end of the range. In all cases, the ultimate question to be asked is whether the person skilled in the art would understand the scope of the monopoly.

“Generally”

The term “generally” raises similar issues to the term “about”. The word indicates that some degree of variation from the specific is intended. For example, a material that is “generally transparent” includes, but is not limited to, those that are totally transparent (although totally opaque would not be included). The degree of variation will depend upon what the person skilled in the art would understand is intended.

The term “generally transverse” did not give rise to any difficulties of construction in Nicaro v Martin (1990) 16 IPR 545.