Dividing the mari is traditionally done by using a thin strip of paper and relational geometry (that is, you first find the circumference of the mari, and then begin locating 1/2's, 1/4's, etc, very easily, by folding the paper). You may either cut the strips yourself, or purchase quilling paper (already-cut thin strips). If cutting your own, attention must be paid to them being straight and even. This is most easily attained with a rotary cutter or a standard paper cutter. Something like  standard copy paper is fine. The strips should be about an eighth of an inch wide - and this can be kind of difficult to cut evenly. Thus, quilling paper provides the advantage of being straight and true - and also being longer. The eleven inch dimension of regular paper will work for most balls but if you do expand into larger ones you will need the extra length of quilling paper. Another option is using narrow ribbon - which can be especially useful for larger mari.

        The strip is pinned to the ball at a place that becomes the north pole (remember to measure to the PIN - not the edge of the strip). It's wrapped around the ball on true dimension to determine the circumference, and cut to this length. Don't remove the strip from the mari until you are completely finished placing locating pins - no mari is perfectly round, so this "north pole" and all related positions are unique to this place. From here the strip will be folded into half, quarters, thirds, fifths, etc. to mark the divisions on the ball. As these divisions are located on the strip by the folds, tiny notches are cut on the folds. Be careful not to make these notches too large so that the strip becomes unstable (it's important to keep it straight as you use it) - or falls apart. The strip is vital to marking divisions and placements on the ball as you progress through the embroidering, and each strip is unique to that ball. Take care of it after the initial marking of the ball - don't discard it until you are completely through with this ball as some designs will call for further marking using it as you proceed.

        If, as you are placing the south pole pin, you discover that it is requiring a constant adjustment with each check of the measuring strip, this could be a good indication that your ball is quite off-round. A round ball will average out its poles fairly quickly - usually within about three or four checks and adjustments. If you are not "on target" within this number of adjustments - cut your losses and begin again since it will not be possible to get accurate divisions. Try pulling the north pole pin and starting over on a different place on the ball... truly. But, if this restart still gives you trouble it is signaling that the mari is not round and will not yield an accurate result. It will only be an exercise in frustration to try to continue - the divisions and markings will be uneven and give a less-than-desired stitching result. Try wrapping the ball some more - add another light layer of thin yarn and thread... being sure to pay attention to roundness. If you still can't pull it into round, then really start over - unravel the ball and reuse the thread. Continuing to try to divide an out-of-round ball will only produce frustration, especially if the division if a complex eight or pentagon. (The more complex and detailed the division, the more critical it becomes to have round mari).

        Division points are indicated by placing pins in the mari at the required places. By traditional teaching and universal vernacular, the north pole of the mari is always indicated with a white-headed pin; the south pole is indicated with a black-headed pin. When inserting the pins, be sure to keep them vertical and straight. It may not seem possible but it's true - the little bit of error introduced if a pin shaft is on an angle can indeed make a difference in the evenness and accuracy of the division and ultimately marking. Remember too - you are working on a sphere and the rules of spherical geometry (not linear geometry) apply. Without going into more involved math rules, think of it this way: spherical geometry magnifies booboos. A little error made "here" expands greatly "over there" (where as in linear, flat geometry, an error "here" is the same as "there"). What color pins are used for other points is entirely up to you.

       When placing pins along the marking strip, be sure that you are consistent. Some people keep to the edge of the strip, placing the pin in the center of the wide edge of the notch along the edge of the strip. Others place their pins into the v of the notch, rather than the edge. Whichever you choose, be sure to stay with that one otherwise you will introduce errors. Don't pull the marking strip out of shape as you lay it on the mari, especially if you cut larger notches (smaller ones will usually be more accurate). Alternately, some people will use only the fold in the strip as the placement indicator rather than cutting a notch. Some people put a pencil mark on the fold.  Others will cut only a slit rather than a notch. The point is that there are various ways to get to the needed result. Choose what is comfortable for you and what works for you.

       When you have placed the pins, a quick way to check for symmetry is to hold it by the north and south pole pins and spin the mari. You should not see "wobble" along the pin paths.

While the most common sections are "even numbered" and divisible by 2, you can run into times when you need to create odd numbers of sections, etc. Here's a nifty shortcut to fold a strip when you need odd multiples.

        All of this being said, many folks have discovered that the good old calculator and tape measure works nicely too, in lieu of folding a paper strip. Not particularly traditional (and will not be received happily by Japanese teachers), but for some people it works better and easier for them. As you develop your technique and experience, you may well find that you can work divisions by eye, to a certain extent, especially for even-numbered Simple divisions, and 8 combination divisions. These divisions use repeated steps of dividing the whole or a portion of the mari in half, and it's quite easy to begin to eyeball these placements. It helps to check your work with a strip or tape but, you'll be surprised at how this can work.