You're not transferring the measurement you take from the pencil exactly to the page, you're using the relationship of the measurements you see in the reference to plan your next steps on the page. It starts with eyeballing your best guess. You have to start with something on the page to relate your measurements to, and adjust. A common unit of measurement is the head unit in figure drawing. When you start a figure drawing, you mark the top of the head, the bottom of the feet, and the half way point on the page, you can then use your pencil to measure your reference. When you sight down the pencil and measure the length of the head, you're checking to see other landmarks that fall within that unit of measurement. The top of the head to the bottom of the chin, is one unit. That unit then can generally measure from the bottom of the chin to the nipple, from the nipple to the navel, from the navel to the crotch, from the crotch to mid thigh, mid thigh to bottom of the knee, bottom of the knee to calf, calf to bottom of the foot. etc. You then have to relate those measured units to the page, creating a new unit of measurement that corresponds to the size drawing you have laid out. You can still use your pencil, you just might need to adjust to find a new measurement that relates to the one you took from the reference so you can break up the space between the top, middle, and bottom lines you've established on the page. Check out the demo from that project to see how Stan measures the reference, and then translates those measurements to the page. Hope this helps! https://www.proko.com/course-lesson/demo-measure-proportions