The purpose of this tool is to help the weaver find a sleying sequence that works for the reed or raddle to approximate the desired Sett. If a reed chart is not readily available, or doesn't have the results that you need, you can use this calculator. This calculator is also convenient is you want to have an average ends per inch/cm but want to do have some skipped dents.
To use, first put in density of your reed or raddle. In the following example, 10 is entered and the "inch" field is selected to indicate 10 dents per inch. For a 1 inch raddle, you'd put 1 in this field, or for the LoftyFiber raddle with 4 spaces per inch, you'd put a 4.
The usage of this calculator involves trial and error. Put in a pattern and click Calculate. You'll be shown the effective ends per inch and ends per cm. One will typically do this several times, tweaking to get the exact SETT they are looking for.
If a pattern space is left empty, then it ignores the entry. A zero in the entry means that the space is skipped. The calculator assumes that the pattern entered will be repeated.
In the example above, a pattern of 1,2,2,2,2 is entered for a 10-dent/inch reed. This calculates at 18 epi.
If I delete the "2" in the last entry, notice that the ends per inch is now calculating at 17.5.
Another usage of this tool is to calculate the average ends per inch when using the "cram and dent" technique. In the example below, two warp ends are sleyed in a dent, skipping the next, putting 4 ends in the next dent and skipping a dent for an effectie 15 epi in a 10-dent reed.
When using a raddle to weave back to front, it's important not to split threading groups. Be sure to put a muliple of the threading groups in each dent when determining the spread. For example, if you wound your warp with two threads at a time, always use 2 or a multiple of two in each dent to avoid spliting the threading group.
If preparing to weave on a Louet loom using the built-in raddle, put 2 in the raddle dents per centimeter (cm) as shown below.
In the above example, if spreading the warp with a 4-4-6 sleying pattern in a Louet reed, the EPI would be 23.71. If you changed to 4-4-6-4-6 as the pattern, the effective EPI would be 24.38. The weaver can continue to try out different patterns to get close to the sett they want.