When carving repetitive designs on rounded objects having good references becomes vital.
The outlines of the carving can be transfered from a paper template thus ensuring that the elements of the design are of consistent size all the way around the work.
Besides needing consistent profiles or outlines one also need to have a reference for depth. Checking for consistency in depth and the form of each part of an element with the work mounted in pitch is impossible and a pain in an engraving vise, as one needs to remove the object from the holding tool in order to see if the work is being done on par with the other side.
To ensure that my carving is consistent all the way around I use a clay model of the design. The model is best made oversize and need not show the finest details. Just the relationship between the components of a design; height, shape and how they meet is enough.
When the one side is done I also take a couple of photos to record the fine details. When the work is turned in the holding tool the clay model and photos of the completed work is enough reference to ensure consistency.