Red boom is always the 1st section. Count 2 and 3 sections when the said boom starts to extend.
For 4, 5 and 6 sections, count when marking stickers appear on the boom.”
For 4, 5 and 6 sections, count when marking stickers on the boom completely appear.
For example, the marking sticker on the 3rd boom completely appear, apply max. lifting capacity of 4 sections.

Please refer to the manual since it differs how to count from model to model.