Inventions. This is a tried and tested invention which works well. As best I know, it is original. I have not found it on the Internet. The alternate rungs make it possible to climb this ladder in a very confined space, as it offers some room for one's knees to move. The rungs are 36cm above each other on the left, and 36cm above each other on the right, and they alternate on opposite sides of the ladder. The rungs each protrude by 10cm. Ensure that a foot has plenty of room on the top rung. The central section is 18cm wide at its widest. A wall serves as a back-rest, 40cm behind the ladder, so that this ladder may be climbed even without hands. OBSERVATION: It combines features of the cage ladder and the pole ladder. Round rungs (as shown here) are easy to manufacture, but they are not easy on bare feet. I hope that explains it! (I don't know where I put my US-units-of-measure hat).