Bowls are designed to travel a curved path, referred to as bias, and was originally produced by inserting weights to one side of the bowl. This is no longer permitted by the rules and bias is now produced entirely by the shape of the bowl. A bowler can recognise the bias direction of the bowl in his hand by a dimple or symbol on one side. Regulations determine minimum and maximum curvature characteristics allowed, but within these rules bowlers can and do choose bowls to suit their own preference. They were originally made from lignum vitae, a dense wood giving rise to the term "woods" for bowls, but are now more typically made of a hard plastic composite material. Usually coloured black, bowls are now available in a variety of colours including a range of fluorescent colours. They have unique symbol markings to identify competitors' bowls, and by regulation have a diameter of about 15 centimetres.
When bowling there are several types of delivery. "Draw" shots are those where the bowl is rolled to a specific location without causing too much disturbance of bowls already in the head. For a right-handed bowler, "forehand draw" is initially aimed to the right of the jack, and curves in to the left. The same bowler can deliver a "backhand draw" by turning the bowl over in his hand and curving it the opposite way, from left to right. In both cases, the bowl is rolled as close to the jack as possible, unless tactics demand otherwise. A "drive" involves bowling with considerable force with the aim of knocking either the jack or a specific bowl out of play - and with the drive's speed, there is virtually no noticeable curve on the shot. An "upshot" or "yard on" shot involves delivering the bowl with an extra degree of weight, enough to displace the jack or disturb other bowls in the head without killing the end. The challenge in all these shots is to be able to adjust line and length accordingly, the faster the delivery, the narrower the line or "grass".
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