There’s a new feature in Calculist that allows you to reference values at different points of the hierarchy in a simple and intuitive way.

parts
  hubs [:] 39
  spokes [:] 14
  rims [:] 50
  tires [:] 20
  handlebars [:] 48
  frame [:] 380
  fork [:] 40
  seat [:] 33
wheels [=] parts.hubs + parts.rims + parts.spokes + parts.tires

Read more on the GitHub wiki.