2. The computer of claim 1 and normally disengaged spring loaded zero set means for automatically returning the belts to a zero time setting, and means for manually engaging said zero set means and said belts to drive said belts to said zero time setting.

3. The computer of claim 1 wherein at least one of said belts includes at least a row of sprocket holes longitudinally distributed along the length thereof and at least one of said pulleys or drums for supporting said one belt, said one pulley or drum including mating sprockets whereby said one belt and said one sprocket cannot slip relative to each other.

4. The computer of claim 1 wherein the rotational movement of each of said shaft sections is controlled by an individually associated color coded knob, and color coding means for identifying the window displaying the data on the belt set by a correspondingly color coded knob. Pg,20

5. The mechanical computer of claim 1 wherein one of said belts carries indicia of time in terms of elapsed hours, and clock means for driving said belts in synchronism with real time as said time is indicated by the indicia on said one belt.

6. The mechanical computer of claim 1 and movable cursor means associated with at least one of the windows and indexed for compensating the reading at said one window for an additional variable.

7. The mechanical computer of claim 1 wherein said clutch means comprises an internal cup-like cavity formed in at least one of the pulleys or drums, said cavity having at least one spline extending in substantially longitudinal alignment with the axis of the pulley or drum, said one pulley or drum being rigidly attached to and turning with one of said sections of one of the shafts, the mating end of another section of said one shaft having a soft rubber collar with an outside diameter corresponding to the inside splined diameter of the drum, whereby said two sections may be interconnected or disconnected by pulling or pushing said knob.

8. The mechanical computer of claim 1 wherein said indicia comprises flight planning said means which may be preset to separately store any selected data.

9. The mechanical computer of claim 1 and key means for interconnecting said shafts with one of said pulleys or drums to cause them to rotate as a unit with the associated shaft, the pulleys or drums on the shaft opposite said interconnected pulleys or drums being free to rotate on one of said shafts, as an idler.

10. The mechanical computer of claim 1 and means for internally lighting said box to display the scales of said indicia on said belts.

11. The mechanical computer of claim 1 and attaching means forming on said housing for mounting said housing on a larger structure.

12. The mechanical computer of claim 1 wherein the removably supported shafts provide means for changing said belts to substitute new scales of indicia.

13. The mechanical computer of claim 1 and zero set means for automatically setting said belts to a predetermined position, said zero set means comprising a pair of springs having different strengths relative to each other, and means whereby a single reset operation first engages said reset means with one of said shafts by pulling against the force of the weaker one of said pair of springs to store energy therein said continued single reset operation driving said belts against the force of the stronger one of said pair of springs to store energy therein, and termination of said single reset operation enables said zero set means to disengage and return to normal under the force of the energy stored in said pair of springs.

14. The mechanical computer of claim 1 wherein each of said shafts include a clutch means, each clutch comprising an internal cup-like cavity in a pulley or drum attached to the end of one shaft section, said cavity being lined with a plurality of spaced parallel splines extending in substantial longitudinal alignment with the axis of the pulley or drum, the mating end of another section of the shaft having a soft rubber collar attached thereto, the outside diameter of said rubber collar corresponding to the inside splined diameter of the drum cavity, key means for interconnecting some of said pulleys or drums to rotate as a unit with the associated shaft, the pulleys or drums on the shaft opposite said interconnected pulleys or drums being free to rotate as idlers on their shafts, each of said belts including a row of sprocket holes longitudinally distributed along the length thereof, each of said pulleys or drums including mating sprockets whereby all of said belts and sprockets are interlocked so that they cannot slip relative to each other, and cursor means associated with at least one of the windows for compensating the reading at said one window for the ambient changes in a variable.