Abstract: A sustaining device for adjustably holding and positioning an article in space which includes a stationary member, a pair of links pivoted thereto and extending therefrom, a floating member pivoted to the outer ends of the links for movement in a vertical plane relative to the first member, a spring connected between said stationary member and said floating member to produce an upward moment to counterbalance the moment produced by the weight of the article and means coordinated with at least one of said members to equalize said moments throughout the range of vertical displacement of said article.