I have 2 sigma's - a BC2006MHR and a a BC1200
Try this link:
or:
"# Multiply the wheel diameter in mm by 3.14 then divide by 1.61 (to convert to mph)
# Measure the distance travelled in one complete turn of the wheel then divide by 1.61 (to convert to mph)."
That being said, the pictograph (hieroglyphics? ) manual does take some getting used to. I do like the fact that they mount with rubber bands(honest!) so you do have to have worry about Zip ties if you want to move it to another bike.