Contractors sometimes use self-propelled aerial lifts on repair and restoration projects and where access is limited. Introduced to the marketplace in the mid 1960's, scissor lifts move a work platform straight up and down. In contrast, variable reach lifts, introduced in the early 1970's, have telescoping or articulated (jointed) booms that can extend up and over obstacles. The key limitation of self-propelled aerial lifts for masonry work is their platform capacity, which ranges from about 500 to 2,000 pounds, depending on model size and type. Consequently, masonry contractors don't normally use these lifts for new construction, where scaffolding is needed to bear the considerable weight of masonry materials. Self-propelled aerial lifts require no set-up or dismantling time and can zoom workers up to a work station in seconds. Thus, contractors can save on labor costs. This labor-saving benefit is especially important on short projects, where unproductive scaffold handling and climbing would consume a larger proportion of the total time.