The professional sheet vinyl layer would likely skip the actions in the following photographs. These preparatory measures would be replaced by a trained eye and reduced to a single spot in the doorway. The installer would rotate the sheet with an experienced eye until it recognises a square and correctly aligned result.
I would not advise the first-time layer to attempt an “align by eye” method. Far safer would be to follow the instructions, making a mental note of all the considerations illustrated.
With many installations of experience, you might attempt to walk into an area like the one illustrated with an unfurled roll under your arm. But you must understand that any successful ‘lay’ will require all the illustrated considerations in the following chapter.
I have placed the tape measure against the wall and run it the full length of the bath, toilet, laundry. I have fastened a mark (atatched) to the tape measure. this mark places the location of the shower area.