In Coffee v. City of Alvin, 641 S.W.2d 597 (Tex. App.--Houston 14th Dist. 1982), writ ref'd n.r.e., 644 S.W.2d 709 (Tex. 1983), after testifying to the value of his land, the owner was cross-examined regarding whether or not he could substantiate or otherwise explain how he determined that value. The owner characterized his dollar figures as "hypothetical" and "as a rule of thumb" which maybe he "pulled out of the air" and maybe "can't substantiate." Id. at 601. The court upheld the trial court's finding that the owner's property value testimony was of no probative value because it was cast in terms of approximation and estimate and unsupported by relevant facts. Id. at 602.