This item was an instrument used to measure time. A wire rope is wound around a drum which unwinds in a fixed time under gravity. A maker which moves horizontally, marks out the time elapsed on a linear scale. This instrument was used before the invention of the pendulum clock for Astronomical measurements at the Madras Observatory.

This item was a magnetic compass which was used by M.K.Vainu Bappu during the visit to Kavalur for site survey. The magnetic compass is a tool used for determining direction on the surface of the Earth. It operates by using a magnetic pointer that aligns itself with the Earth's magnetic field. This type of compass is the oldest and most commonly used in various forms of transportation such as aircraft, ships, and land vehicles. The Earth's magnetic field acts as an enormous bar magnet with a North-South field that causes freely moving magnets to take on the same orientation. Although the direction of the Earth's magnetic field is not entirely parallel to the North-South axis of the globe, it is close enough to make an uncorrected compass a reasonably good guide. The inaccuracy, known as variation (or declination), varies in magnitude from point to point on Earth.

This item was an instrument used for measuring the intensity of a light source. It uses a light-sensing device that is calibrated to express intensity in a standard unit. Some optical elements such as lens etc. are also employed to incerase the sensitivity of the instrument.

This item was a optical instrument named as Stereoscope. Stereoscopes are apparently those optical devices that help to view the two images separately and with relaxed eyes. There are two types of stereoscopes as: lens or pocket stereoscopes and mirror stereoscopes. Lens or pocket stereoscopes are great for viewing the whole overlap area of prints up to 9 cm × 13 cm or parts of larger patterns. On the other hand, mirror stereoscopes were designed to accept standard 23 cm × 23 cm metric air photos and work well with A4/US letter-sized prints. Most models come with magnifying options up to eight times, which is pretty impressive. One cool thing about mirror stereoscopes is that they are large enough to allow the analyst to draw beneath them, so it is possible to trace objects identified in the stereoview with a pen onto one of the images or a transparent overlay. However, it's important to remember that this sketch wouldn't have the geometric properties of a map as it contains all distortions present in the base image.

This item was an instrument used in surveying land, alignment, testing, and calibrating optical Instruments. It is basically a refracting telescope. Whose optical elements tilt angles with high accuracy of the order of arcsecs.

The item is a 6 inch transit circle. The transit circle is an instrument used to determine the declination of stellar onjects. It consists of a circular scale kept perpendicular to the rotating axis of a telescope tube.