Laws of Cricket 1947 Code (Fourth Edition) - Law 47
The Umpires shall not order a Batsman out unless appealed to by the other side which shall be done prior to the delivery of the next ball, and before "Time" is called under Law 18. The Umpire at the Bowler's wicket shall answer appeals before the other Umpire in all cases except those arising out of Laws 38 or 42 and out of Law 41 for run out at the Striker's wicket. In any case in which an Umpire is unable to give a decision, he shall appeal to the other Umpire whose decision shall be final.
Notes on Law 47
1. An appeal, "How's that?" covers all ways of being out (within the jurisdiction of the umpire appealed to), unless a specific way of getting out is stated by the person asking. When either umpire has given a batsman "Not out" the other umpire may answer any appeal within his jurisdiction, provided it is made in time.
2. The umpire signals "Out" by raising the index finger above the head. If the batsman is not out, the umpire calls "Not out".
3. An umpire may alter his decision provided that such alteration is made promptly.
4. Nothing in this Law prevents an umpire before giving a decision from consulting the other umpire on a point of fact which the latter may have been in a better position to observe. An umpire should not appeal to the other umpire in cases on which he could give a decision, merely because he is unwilling to give that decision. If after consultation he is still in any doubt, the principle laid down in Law 46 applies and the decision will be in favour of the batsman.
5. The umpires should intervene if satisfied that a batsman, not having been given out, has left his wicket under a misapprehension.
6. Under Law 25 the ball is "Dead" on "Over" being called; this does not invalidate an appeal made prior to the first ball of the following "Over", provided the bails have not been removed by both umpires after "Time" has been called.
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