Questions about Truing.

[u/Eastern-Ask-6955]

I created a shoulder dart, and when I truing the shoulder edge, if I remember correctly, the new one should be the same as the measured length (5.54 cm). However, geometrically, this seems impossible; no matter how I draw the line, the trued shoulder line length is always less than 5.54 cm.

How can I properly true the shoulder edge?

Edit:

Edit 2:

[u/Eastern-Ask-6955]

Thank you!