A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Geoffrey Kolbe
Date: 2019 May 5, 00:44 -0700
"If however two are inward and one is outward, or vice versa then you get the excentre corresponding to the odd one out!"
But.... if (as per your initial consideration) there is no random error, only systemic error, then the error will be constant both in amount and sign for all three sightings. So, ALL PLs will be 'away' by the some amount which is the same, or ALL PLs will be "towards" by the same amount. That being the case, the true position will be centre of the incircle in ALL (both) cases...?