Rotary slide rule for topographic calculations

A rotary topographic calculator comprising:

• a baseplate having an annular scale for indicating rod readings;
• and
• a rotatable conversion unit mounted on said baseplate and operable to directly convert rod readings on said scale into corresponding elevations relative to a predetermined reference elevation,
• said unit being provided with three annular elevation scales of different radii within said rod reading scale and concentric therewith, and including three independently rotatable discs coaxial with said scales for aligning said elevation scales in a selected orientation to indicate elevation relative to said predetermined reference elevation,
• one of said elevation scales covering a range of numerical values formed by the units and tens digits of elevation, a second of said elevation scales representing the hundreds digit of elevation, and the third elevation scale representing the thousands digit of elevation,
• said one elevation scale being concentrically arranged on one of said discs and numbered inversely with respect to said rod reading scale, and said one disc being rotatable to an operational setting radially aligning a predetermined rod reading with the numerical value on said one scale corresponding to a known elevation, whereby other rod readings may be directly converted into corresponding elevations by reading the aligned numerical values on said one elevation scale in conjunction with the digits of said known elevation read from said second and third scales or, conversely, elevations may be converted into rod readings,
• said second elevation scale being concentrically arranged on said one disc within said one elevation scale, a second of said discs overlying said second scale and having a window therein for revealing a selected hundreds digit.

A rotary topographic calculator comprising:

• a baseplate having an annular scale for indicating rod readings;
• a rotatable conversion unit mounted on said baseplate and operable to directly convert rod readings on said scale into corresponding elevations relative to a predetermined reference elevation,
• said unit being provided with three annular elevation scales of different radii within said rod reading scale and concentric therewith, and including three independently rotatable discs coaxial with said scales for aligning said elevation scales in a selected orientation to indicate elevation relative to said predetermined reference elevation,
• one of said elevation scales covering a range of numerical values formed by the units and tens digits of elevation, a second of said elevation scales representing the hundreds digit of elevation, and the third elevation scale representing the thousands digit of elevation,
• said one elevation scale being concentrically arranged on one of said discs and numbered inversely with respect to said rod reading scale, and said one disc being rotatable to an operational setting radially aligning a predetermined rod reading with the numerical value on said one scale corresponding to a known elevation, whereby other rod readings may be directly converted into corresponding elevations by reading the aligned numerical values on said one elevation scale in conjunction with the digits of said known elevation read from said second and third scales or, conversely, elevations may be converted into rod readings;
• a rotatable disc member carried by said baseplate and coaxial with said three discs;
• and
• an annular depth scale concentrically arranged on said disc member and graduated to indicate depth of cut and depth of fill in progressively increasing amounts in opposite directions away from a zero mark,
• said disc member being rotatable to a position radially aligning said zero mark with a selected rod reading or numerical value of elevation on said one elevation scale, whereby the depth scale then indicates the cut or fill at other corresponding radially aligned elevations on said one elevation scale.

A rotary topographic calculator comprising:

• three superposed plate elements mounted for relative rotation about a predetermined axis;
• an annular scale arranged on one of said elements in concentric relationship with said axis and graduated to indicate a range of rod readings;
• an annular elevation scale arranged on a second of said elements in concentric relationship with said axis and graduated to cover a range of numerical values corresponding to said range of rod readings, and being numbered inversely with respect to said rod reading scale;
• and
• an annular depth scale arranged on the third of said elements in concentric relationship with said axis and graduated to indicate depth of cut and depth of fill in progressively increasing amounts in opposite directions away from a zero mark, the angular increments between the graduations of said depth scale being equal to the same units of measurement as like angular increments on said rod reading and elevation scales,
• said one and second elements being relatively rotatable to an operational setting radially aligning a predetermined rod reading with the numerical value on said elevation scale corresponding to a known elevation,
• said one, second and third elements being relatively rotatable to a position radially aligning said zero mark with a selected rod reading or elevation, whereby the depth scale then indicates the cut or fill at other corresponding radially aligned elevations.