Automatic Site Levels

Automatic (Dumpy) Site Levels

Builders and Contractors will normally have an automatic level or 'dumpy' level to assist them in the setting of site levels.
They work on the principle - that the 'kit' is set up in such a way that it defines a horizontal plane at a known height around 360° from which accurate measurements can be taken to establish point levels. An automatic level uses line of sight, albeit enhanced somewhat via the telescope, They also rely on a graduated staff to measure the difference between the level plane and the point to be established.
The 'kit' is usually mounted on a tripod and will have some adjustment mechanism that allows the 'kit' to be set to true horizontal. The most common system for checking horizontality is a circular bubble tube. The foot-screws of the unit are adjusted until the bubble is cantered within the bubble tube. Different automatic levels have differing degrees of accuracy. The bubble-set kit is usually taken as accurate to with 10 minutes (one-sixth of a degree; there are 60 minutes to one degree) and should be accurate enough for most site groundwork's, landscaping and paving jobs. There are more accurate levels available for exacting work where precision is vital, but, of course, they cost a lot more.
The level unit is set-up in a position which gives a clear view of all points to be levelled, or as many as is feasible under site conditions. Each position where the level is set-up is referred to as a 'station', and stations may be marked for future reference by means of a timber peg, steel pin, brass tag or paint mark as befits the conditions. Marking of stations in this way allows levels and angles to be checked at a later date if a discrepancy is found.