Measurements - Need some help

[puzzledpaul]

@ppaul

I was with you up until tangential. Sorry.

Obviously mr / mrs /ms etc google would be of use with this ... but a real world example would be

wine bottle lying on its side on a table top
view wine bottle from bottom ...at table top height, so see bottle end as a circle, table top as a line.
(line of) table surface forms a tangent to the circle ... ie a straight line 'just kissing' - at a single point (line along bottle for any pedants reading -assuming cylindrical bottle) - the circle.

Therefore 'drawing a line blah blah ...' means drawing a line from some point - towards a circle - such that it (the line) just -and only just - touches the circle.

best tested with an empty bottle as it'd be a crying shame / waste if the other sort rolled off and bottle got broken

pp