Compound bows are the newest type of bow, and almost anything is allowed as long as it is not electronic. These bows consist of eccentric cams to make drawing the bow easier. The limbs of a compound bow are much stiffer than those of a recurve bows or longbow. This limb stiffness makes the compound bow more energy-efficient than other bows, in conjunction with the pulley/cams. Archers using compound bows most commonly use a release aid to hold the string and release it precisely, although finger tabs are also popular with compound bows, especially among older archers who have used finger tabs when shooting recurve bows. The release aid attaches to the bowstring just below the nocking point or at the D loop and permits the archer to release the string by the use of some form of trigger. Wrist release aids are good for alignment with many archers finding it easier to align bow hand, trigger hand and rear elbow. They are also good for archers who struggle with sight marks as the anchor position increases distance from eye to release hand.