A roll turner is much better for the eggs than having them standing on end. The ducks themselves turn the eggs often- in an incubator most people mark eggs so you know how far a 180 degree turn is. The mother ducks dont mark their eegs- they just give them all a flip. AS long as when you turn them- they arent on one side for extended periods- and they lay on each side equally- IE: turning an odd number of times each day- so each night ( the longest time they go unturned usually ) they will have equal time on either side. While turning at regular intervals is important- it is not always possible- but try to make sure that they just have equal time on each side.