Which one the following statement is correct about the sign convections?
1. All distances are measured from the pole.
2. Distances measured in the direction of incident rays are taken as positive while in the direction opposite of incident rays are taken negative.
3. Distances above the principle axis are taken positive and below the principle axis are taken negative.
4. Distances measured in the direction of incident rays are taken as negative while in the direction opposite of incident rays are taken positive.1
Only 1
2
1, 2 and 3
3
1, 3 and 4
4
Both 2 and 3