Oops! My bad....I didn't look thoroughly enough at your website, because I missed your (obviously well-considered) Givens and Druthers page. And until this post, I hadn't paid attention to the compass you included on your previous posts. I apologize for my muddled comments. Upon re-reading them today, I realized I had compounded the incoherence caused by my incorrect compass points by incorrectly mislabeling which deck I was talking about in 2 places and by not even being consistent in what direction I (mistakenly) called "North". Here is a revised version of how I should have described my understanding of how trains would move over your layout (revisions in red): "Westbound trains will leave the westbound staging yard on the lower level, go up the helix to the middle level, travel North (left to right as you face West) at the front of the middle level, then cross South (right to left) at the back of the middle level, go up the helix to the upper level, then North (left to right) across the upper deck, continue clockwise around the layout back to the helix by going over the Nod-Under Bridge, travel down the helix to the lower deck and past the Ready Tracks, but bypass the Westbound staging by cutting across the base of the peninsula to enter the west end of the Eastbound Staging Yard ." Assuming 200 inches of Mainline from helix to base of the lower level peninsula, 200 inches to the Westbound Staging side of the peninsula, 200 on the Eastbound Staging side of the peninsula, 200 on the inside of the support column shelf, and 200 on the outside of the support column shelf, plus a possible 200 from the outside of the support column shelf through the backdrop, across the base of the peninsula (bypassing both staging yards) plus 200 inches in the Ready tracks Yard, yields 1400 inches of possible lower level mainline. Rising 14 inches with a 2% grade yields a 700 inch run in the helix from lower to middle level. Assuming similar numbers for the middle level, gives a 1400 inch long mainline (but could be 1600 inches,if the elevated line back to the helix runs around the tip of the peninsula instead of across the base of the peninsula). Rising to the upper level gives another 700 inches of mainline. Running north (left to right facing west) from the helix to the tip of the support shelf gives 800 inches, and across the Nod-Under Bridge adds 50 inches more for a total of 850 inches mainline on the upper deck. Down the helix to the lower deck is 1400 inches. If you run from lower level Westbound staging to upper level Nod-Under Bridge and back to down to lower level Eastbound staging, then the mainline would be: Lower level 400, helix 700, middle level 1400 (or 1600), helix 700, upper level 850, helix 1400, and lower level 400 inches...Total run = 5850 inches (or 6050 inches). 800 inches (800/6050=13%) in staging yard or ready track yard; 2800 inches (2800/6050=46%) in the helix; 2450 inches (2450/6050=41%) in sceniced layout. It would be possible to have a larger percentage of mainline visible and sceniced if: 1. one staging yard was repositioned from the lower level peninsula to visible staging in a sceniced yard on the inside of the lower level support column shelf (where there is ample headroom) and there was a yard lead to feed tracks at the west (left) end of the shelf, 2. a second visible staging (sceniced) yard to the inside of the upper level of the support column shelf with a lead feeding tracks at the east (right) end of the yard (so both yards could be switched without operators interfering with each other), 3. the entire lower level was sceniced, including outside of the support columns, although there would not be much (any?) switching done there because of the ceiling height. A Mainline could run 800 inches from the lower level support column shelf to the helix, 700 inches up the helix, 1600 inches on the middle level, 700 in the helix, and 800 from helix to upper level inside support column shelf (or 1200 if it crosses the front edge of the shelf inside of the support column shelf at 59 inches and then loops around to the outside of the support column climbing toward the basement door and curving back through the backdrop to enter the upper level visible staging yard on the inside of the support column shelf at 61 or 62 inches). This plan would yield 4600 or 5000 inches of mainline: 1400/4600=30% or 1400/5000=28% in the helix and 70% or 72% visible/sceniced. [4600 inches/396inches per scale mile = 11.6 scale miles of mainline] If a branchline interchange/junction was established one side of the middle level peninsula or the other, it would be possible to run a branchline turn from the middle level peninsula north to the middle level support column shelf (600 inches) and then on the middle level elevated track back south (400 or 600 inches)to take the helix up to the upper level (700 inches), and circle (north) across the upper level to go over the Nod-Under Bridge at 62 or 63 inches (1250 inches) and take the helix down to the lower deck (1400 inches) and across to the visible staging on the inside of the support column shelf (800 inches). 2100/5150=41% or 2100/5350 = 39% in the helix and 59 or 61% visible/sceniced. If the branchline was worked as a turn, then the run would be 26 scale miles long.