Indicating instruments

In an indicating instrument having an instrument scale and in which indication of the value of a variable is provided partly by an index that is arranged to rotate through more than one revolution to pass the zero or other datum of the instrument scale in response to successive changes of unit quantity in the variable, and in which a member that bears graduation markings in terms of the said unit quantity is arranged for movement relative to the scale in accordance with rotation of the index, but at a reduced speed, to provide coarse indication of the value of the variable in terms of said unit quantity;

• the improvement wherein the graduated member is a disc mounted for rotation coaxially with the index, the said markings being distributed around a circumferential margin of the disc, the said disc being located to be viewed against the datum of the scale thereby to provide the coarse indication by reference to the positioning of its said graduation markings relative to the same datum as used for the index, the index, throughout a limited sector of its rotation up to the datum, pointing to the said disc between two of its graduation markings to emphasize which of those markings is appropriate to the coarse indication, the scale having an aperture therein that breaks into the scale at said datum, the said disc being located behind the scale to present the said markings thereon for viewing within the aperture, and the aperture being dimensioned to limit view of the disc to a small sector of its said circumferential margin, the particular sector of said margin and the particular markings visible within said aperture at any time being dependent on the rotational position of the disc at that time.

An indicating instrument for providing an indication of the value of a variable, comprising:

• a scale having an arcuate window therein, scale having a zero datum located against an arcuate boundary of the window;
• an index mounted for rotation to sweep over said scale, the rotational sweep of said index passing closely along said arcuate boundary of the window throughout a final sector of each complete revolution of the index to said zero datum;
• sensor means responsive to said variable to rotate the index to an angular displacement from the zero datum dependent on the value of said variable, said sensor means being operable to displace the index angularly from said zero datum through more than one revolution depending upon said value;
• a rotatably-mounted member bearing a sequence of numerical markings distributed angularly from one another, said member being located behind the scale to present a limited sector of the said sequence of markings for view through the window, the particular sector of said sequence visible through the window being dependent on the angular position of the said member relative to the scale;
• and further means coupled to said sensor means for rotating the said member relative to the scale in accordance with, but at a slower speed than, the rotation of said index to bring successive ones of said sequence of numerical markings to said zero datum upon each successive revolution of the index past the zero datum, said further means being operable to rotate said member past said zero datum in opposite sense to the rotation of said index.

An altimeter comprising:

• a scale having an arcuate window therein, said scale having a zero datum located intermediate the length of the window and against an arcuate boundary thereof;
• an index mounted for rotation to sweep over said scale, the rotational sweep of said index passing closely along said arcuate boundary of the window throughout a final sector of each complete revolution of the index to said zero datum;
• manometric sensor means to provide a measure of altitude;
• drive means coupled to said manometric sensor means to rotate the index to an angular displacement from the zero datum dependent on the magnitude of said measure of altitude, said drive means being operable to displace the index angularly from said zero datum through more than one revolution depending upon said magnitude;
• a rotatably-mounted disc bearing a sequence of numerical markings distributed angularly from one another circumferentially of the disc, said disc being located behind the scale to present a limited sector of the said sequence of markings for view through the window, the particular sector of said sequence visible throughout the length of the window including at least two of said markings and being dependent on the angular position of the said disc relative to the scale;
• and further means intercoupled with said drive means to rotate the said disc relative to the scale in accordance with, but at a slower speed than, the rotation of said index to bring successive ones of said sequence of numerical markings to said zero datum upon each successive revolution of the index past the zero datum, said further means being operable to drive said disc past said zero datum in opposite sense to said index.

In an indicating instrument having an instrument scale and in which indication of the value of a variable is provided partly by an index that is arranged to rotate through more than one revolution to pass the zero or other datum of the instrument scale in response to successive changes to unit quantity in the variable, and in which a member that bears graduation markings in terms of the said unit quantity is arranged for movement relative to the scale in accordance with rotation of the index, but at a reduced speed, to provide coarse indication of the value of the variable in terms of said unit quantity:

• the improvement wherein the said graduated member is located to be viewed against the datum of the scale thereby to provide the coarse indication by reference to the positioning of its said graduation markings relative to the same datum as used for the index and wherein the index, throughout a limited sector of its rotation up to the datum, points to the graduated member between two of its graduation markings to emphasize which of those markings is appropriate to the coarse indication, the scale having an aperture therein that breaks into the scale at said datum, the said graduated member being located behind the scale to present the said markings thereon for viewing within the aperture, the particular markings visible within the aperture at any time being dependent on the position of the said graduated member at that time, the said aperture having a width to provide that at least two of the said graduation markings are visible within the aperture at any time, said aperture having a first portion that occupies a part of said scale extending up to said datum and having a second portion that occupies another part of said scale extending from said datum, said graduated member bearing graduations intermediate said markings for viewing within said first portion of the said aperture, and said second portion of the said aperture having a step therein to obscure from view those of said intermediate graduations that would otherwise appear to view within said second portion of the aperture.

An indicating instrument for providing an indication of the value of a variable, comprising:

• a scale having an arcuate window therein, said scale having a zero datum located against an arcuate boundary of the window;
• an index mounted for rotation to sweep over said scale, the rotational sweep of said index passing closely along said arcuate boundary of the window throughout a final sector of each complete revolution of the index to said zero datum;
• sensor means responsive to said variable to rotate the index to an angular displacement from the zero datum dependent on the value of said variable, said sensor means being operable to displace the index angularly from said zero datum through more than one revolution depending upon said value;
• a disc mounted for rotation coaxially with said index, said disc bearing a sequence of numerical markings distributed angularly from one another, said disc being located behind the scale to present a limited sector of the said sequence of markings for view through the window, the particular sector of said sequence visible through the window being dependent on the angular position of the said disc relative to the scale;
• and means for rotating said disc relative to the scale in accordance with, but at a slower speed than and in opposite sense to, the rotation of said index to bring successive ones of said sequence of numerical markings to said zero datum upon each successive revolution of the index past the zero datum.

An indicating instrument for providing an indication of the value of a variable, comprising:

• a scale having an arcuate window therein, said scale having a zero located against an arcuate boundary of the window;
• an index mounted for rotation to sweep over said scale, the rotational sweep of said index passing closely along said arcuate boundary of the window throughout a final sector of each complete revolution of the index to said zero datum;
• sensor means responsive to said variable to rotate the index to an angular displacement from the zero datum dependent on the value of said variable, said sensor means being operable to displace the index angularly from said zero datum through more than one revolution depending upon said value;
• a rotatably-mounted member bearing a sequence of numerical markings distributed angularly from one another, said member being located behind the scale to present a limited sector of the said sequence of markings for view through the window, the particular sector of said sequence visible through the window being dependent on the angular position of the said member relative to the scale;
• means for rotating the said member relative to the scale in accordance with, but at a slower speed than and in opposite sense to, the rotation of said index to bring successive ones of said sequence of numerical markings to said zero datum upon each successive revolution of the index past the zero datum;
• said zero datum lying intermediate the length of said window whereby said window has a portion thereof extending from the said zero datum throughout an initial sector of each complete revolution of the index, said member bearing graduations intermediate said numerical markings for view within said window, and said instrument including means to obscure said intermediate graduations from view within said portion extending from said zero datum.