5 knobs | 3 |- | 6 knobs || ~240 |- | 7 knobs || 18 |- | 8 knobs | 9 |- | 9 knobs || 3 |- | 10–55 knobs || 52 |- | 70–160 knobs || 14 |} Ornamentation The decoration used falls into three categories: those with spirals those with concentric circles those with patterns of straight incised lines and hatchings More than one design is used on the same ball and the standard of artwork varies from the extremely crude to the highly expert which only an exceptionally skilled craftsman could have produced. Some balls have designs on the interspaces between the knobs which must be significant in the context of the speculated use of these artefacts. Twenty-six of the six-knobbed balls are decorated. The Orkney examples are unusual, being either all ornamented or otherwise unusual in appearance, such as the lack, bar one example, of the frequently found six-knobbed type. Metal may have been used to work some of the designs. The Towie ball has some design similarities with the carvings on the Folkton Drums. These were found in a tumulus in England and are made of chalk with elaborate carvings, among which are distinct oculi or eyes. Concentric carved lines on stone balls appear to be stylised oculi. This ball also has a roughly triangular arrangement of three dots in an interspace between the knobs. This appears to be identical to the arrangement of dots found on the Parkhill silver chain terminal ring, found near Aberdeen, a Pictish artefact. It is possible that the dots represent a name, as some of the Pictish symbols at least are thought to represent personal names. Spirals or plastic ornament which is similar to Grooved Ware is found on the Aberdeenshire examples, this being a type of late Neolithic pottery not known in the north-east but common in Orkney and Fife. The New Grange carvings in Ireland show strong similarities to those found on some balls. A continuous spiral is found on one and elements of chevrons, zig-zags and concentric triangles are also found, stimulating comparisons with petrosomatoglyph symbolism. Mostly the different knobs have different or sometimes no ornamentation. A 'golf-ball' variety of ornamentation is found on a few balls. The carving does not appear to have any practical purpose in general, however it has been suggested that one type, with very distinct knobs, was used for