announcement: Double-tracking Project - First Right of Refusal as Sub-Contractors. 30 October 2003. (原始内容存档于24 July 2011). Statement on the DoubleTracking Electrification
(页面存档备份,存于互联网档案馆) Gary Seronik, "Build a Tracking Platform for Your Camera" in Sky & Telescope, June 2007, p. 80. Trott, Dave. The Double Arm Barn Door with original