In the following image:
$R1$ is positive as it is measured from the left surface and extends to the right.
$R2$ is negative as it is measured from the right surface and extends to the left.
For a double convex lens the radius R1 is positive since it is measured from the front surface and extends right to the center of curvature. The radius R2 is negative since it extends left from the second surface (Source).
So extending left is negative, extending right is positive, correct?
However, in this image:
Firstly they have R1 labelled on the opposite side to the first image.
$R1$ and $R2$ both extends to the left, so wouldn't these be negative?
Why have they labeled them positive?