Levels
A 'regular' height measurement is essentially a distance measurement but then vertically. For those instruments, please see 'Distance'. The instruments that measure height all meaasure a relative height using either a direct distance or a pressure difference. The latter type is the 'barometer' with a height indication.
The instruments that measure distance (height difference) are level instruments of which the carpenter level is the most well known at home. In my collection there are four types of levelling instruments:
- Hand levels where the leveling is done 'by hand' i.e. the device is held in the hand and levelled by tilting the hand
- Dumpy levels where the instrument is manually levelled using a tilting arrangement of the instrument relative to the base of the instrument whcih is fixed to a tripod
- Automatic levels where the instrument is automatically leveled when within a certain degree of the true level
- Fluid levels that use a fluid between two ends of the measuring device (usually through a hose) to indicate a height difference.
Subcategories
-
Hand level
The hand level is the simples of all levels and include the carpenters level (a long bar with a tubular level attached). In the United States the optical hand level is used a lot in construction. It is a levelling vial combined with a sight tube to allow measurements over longer distances than with a regular level. It is essentially similar to an Abney level without the option to measure vertical angles.
-
Tilting levels
The tilting (or dumpy) levels require a two-step approach to setting them truly 'level'. The first is the coarse adjustment using the buble level on the base. Then they are fine adjusted using a tilting screw that angles the telescope with the accurate tubular level attached to it.
Depending on the instrument the tubular level is viewed directly using for example a mirror or both ends of the bubble are brought into coincidence using a prism. The more accurate geodetic levels can be 'reversed' (i.e. turned upside down) to cancel out any non-parallism between the telescope axis and the level. A number of level instruments are also equipped with a (coars) horizontal circle to allow measurement of horizontal angles with some accuracy. Depending on the instrument these are either in the 360 degree or 400 gon system (both representing a full circle).
Most of the tilting levels that I own are from Wild Heerbrugg are all designated 'N' for Nivellier and then depending on whether they have a horizontal circle a 'K' - Kreiss. The final number is then the series where the larger number is more accurate (a '1' serie is less accurate than a '2' etc).
-
Automatic levels
The automatic level uses an arrangement within the body of the instrument that sets the line of sight horizontal (perpendicular to gravity) automatically when the instrument is within a certain angle from being level. Often this is a prismatic arrangement.
The instrument has only a single bubble level to bring the instrument to within the required degree of the true level for the automatic system to do its job. A number of level instruments are also equipped with a (coars) horizontal circle to allow measurement of horizontal angles with some accuracy. Depending on the instrument these are either in the 360 degree or 400 gon system (both representing a full circle).
Most of the automatic levels that I own are from Wild Heerbrugg are all designated 'NA' for Nivellier - Automatik and then depending on whether they have a horizontal circle a 'K' - Kreiss. The final number is then the series where the larger number is more accurate (a '1' serie is less accurate than a '2' etc).
-
Hydrostatic
The fluid level uses the law of corresponding states to show the height difference between two glass vials connected by e.g. a hose. Depending on their construction they can be very accurate. They are used in conditions where the distances are very long or an optical level is impractical.
