Balkline adds a position rule to the ordinary carom. You still contact both object balls with your cue ball, but must also manage where the object balls remain. The important question is not merely how many points you have made; it is which zone state applies before the next stroke.
What the two numbers identify
In 47/2 and 71/2, the first number names the line distance in centimetres and .2 identifies the two-stroke discipline. UMB Article 73 describes nine areas for 47/2 and six for 71/2. The 47/1 version uses the 47 cm layout with a one-stroke restriction. These are discipline names, not match distances or averages.
Exit on the second stroke, not the third
In a two-stroke zone, the first carom may leave both object balls inside. On the second stroke, at least one must leave that zone for the carom to be valid. It may return during the same stroke. You do not get two retained points followed by an obligation to leave on a third. In 47/1, the required exit already applies on the first stroke with both object balls inside.
Read the position before playing
The UMB distinguishes entry, inside and astride positions. Object balls on opposite sides of a line are astride; the cue ball's location does not determine their zone. A ball exactly on a line is treated disadvantageously to the player. Anchors are additional small areas astride the ends of balklines at the cushions, with their own applicable zone restriction; they are not simply the four table corners.
A two-stroke observation exercise
Away from a match, identify a marked area and start with both object balls inside it. Before each attempt, say whether an exit is required. Record three things: did the cue ball touch both balls, did an object ball leave the area, and where did both finish? Count the carom only if all applicable conditions are met. Do not draw your own marks on a club cloth; use an approved training layout or a diagram.
Why this differs from three-cushion
Balkline rewards controlling a scoring position while satisfying a zone rule; three-cushion requires three cushion contacts before the second object ball. Neither score measures the other's skill directly. The exercise above is our way of reading the official rule, not a federation qualification test. For a match, use the referee's announcements and the organizer's current discipline rules.
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