QG-L4: 1st QG-Quasi Euler line The 1st QG-Quasi Euler line is the line through QG-P4 (1st Quasi Centroid), QG-P5 (1st Quasi Circumcenter), QG-P6 (1st Quasi Orthocenter) and QG-P7 (1st Quasi Nine-point Center). This line is also mentioned in Ref-15i and Ref-30 (page 290). Coefficients: The coefficients of QG-L4 can be easily derived by calculating the Crossdifference (see Ref-13, keyword: crossdifference) of QG-P4 and QG-P5. Properties: QG-L4 is the Euler line of the 1st QG-Quasi Diagonal Triangle QG-Tr1. The 1st QG-Quasi Euler line QG-L4 // the 2nd QG-Quasi Euler line QG-L5. QG-P1 is the Railway Watcher (see QA-L-1) by the 1st QG-Quasi Euler line QG-L4 and the 2nd QG-Quasi Euler line QG-L5 (note Eckart Schmidt).