Making a tangent S over top head restraint which is vertical to datum line. Namely, the distance from poit R to tangent S is the height of headstraint.是什么意思_Making a tangent S over top head restraint which is vertical to datum line. Namely, the distance from poit R to tangent S is the height of headstraint.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句