Older CMG models like the ones launched with Skylab in 1973 had limited gimbal travel between fixed mechanical stops. On the Skylab CMGs the limits were plus or minus 80 degrees from zero for the inner gimbals, and from plus 220 degrees to minus 130 degrees for the outer ones (so zero was offset by 45 degrees from the centre of travel). Visualising the inner angle as 'latitude' and the outer as 'longitude', it can be seen that for an individual CMG there were 'blind spots' with radius 10 degrees of latitude at the 'North and South poles', and an additional 'blind strip' of width 10 degrees of 'longitude' running from pole to pole, centred on the line of 'longitude' at plus 135 degrees. These 'blind areas' represented directions in which the rotor's spin axis could never be pointed.