In the 1980s,when at Eastern Radar,I saw a very slow moving primary return around Beeno (intersection of B1 &A37),so I asked one of the military controllers( they had a height-finding facility) to 'pull a height'.IIRC,it came back as around FL 200,and was thought to be a WX balloon.Fortunately there was no conflicting traffic at the time & it drifted off to the North East.