addendum circle [机] 齿冠圆
Addendum \Ad*den"dum\, n.; pl. {Addenda}. [L., fr. addere to
add.]
A thing to be added; an appendix or addition.
{Addendum circle} (Mech.), the circle which may be described
around a circular spur wheel or gear wheel, touching the
crests or tips of the teeth. --Rankine.