(If there are objections, I'll remove this, but I was wanting to keep track of certain terms I'd encountered.) 'depth of scye' - A vertical distance (in some historical pattern systems), from the neck of the nape to a horizontal lane between the armpits typically at the back. (see Measurement: ?)
'fish' A removed section of fabric along a defined axes, the removal being formed by symmetrical curved arcs, drawn such that the widest seperation of the arcs is of a defined width, lying perpendicular to the defined axes, at a defined point. Not to be confused with a dart.
To draft this in seamly. ...
'scye' - A curve typically representing an armhole in a design. ( see also https://en.wiktionary.org/wiki/scye), Typically formed from number or other arcing or curved edges on pattern peices, which combine to form the curve when the garment design is constructed. (See also measurement:L19-22,L29, L28)
'seat' - A measurement representing the maximum width needed to accommodate the widest point below the waist, (see also Measurement: G08,G09)
to 'square' from a line is to draw perpendicular to it, squaring from a vertical line means you draw horizontally to or from it a given point. (Seamly 2D has a tool for creating a point, perpendicular to a given line.)