Yes, indeed! Those problems are why Lennard Zinn's technique uses a thick dowel that will be hard to bend, and a sensitive level on the dowel to see when it's level. A very resourceful person could rig up a device to perhaps allow a plumb line to be attached so that you could capture the vertical distance without an assistant and then measure the length of string with the bob and get the PBH. But, more steps allows for more errors.