![]() ![]() In short, vertical measurements become known by measuring elevation off a mother-of-all-datums. How are the vertical measurements of a surveyor’s map “known”? In other words, the pin’s location in three dimensional space must be measured and associated with the known vertical measurements of the site, usually recorded in a surveyor’s map. Once a benchmark is set by locating a pin on the building site, that pin must then be correlated with the building site. All of that said, measuring instruments that enable an easy check to the project benchmark using laser technology or sonar technology is becoming more and more prevalent on job sites and is improving the accuracy and quality of the job sites that use them. Nonetheless, to be exercising control, you must be at least regularly checking against the benchmark to ensure that you are not gathering measurement errors as the work progresses. However, it could be extremely tedious and not at all efficient to constantly measure off the benchmark. To me, this is a relative way of placing, as opposed to an absolute way of placing, which would be to place or set things by measuring off the benchmark each time, which is turn would eliminate the accumulation of measurements and reduce the gathering of error. In construction, the placing and setting of things by measuring off a previously placed or set thing is common practice. For instance, the fractions of inches lost or gained when rounding individual measurements could, when summed, make a very real difference in comparison to what an overall measurement would yield. When it comes to measuring, error tends to develop in accumulated measurements. The head of that pin becomes the benchmark from which all vertical measurements are taken using measuring devices like a transit or laser level, that pin becomes the ultimate point of control in a vertical system of measurements. nail) into something of relative permanence, be it pavement or a tree or a masonry wall or any substantial thing that is immobile. How is a Benchmark Datum Established?Ī benchmark datum can be established quite arbitrarily by simply driving a sturdy pin (a.k.a. In complex operations, there may be a system of benchmarks called out, but in a smaller operation a single benchmark will often be isolated as the “ground zero“ of the system, the primary plane of reference, the sun in the solar system, the queen of the hive. But in common use of the term, it is not just any datum – in a system of vertical measurements, a benchmark is a special datum. It is true that a benchmark is a datum in and of itself. ![]() Some folks use the word benchmark interchangeably with the word datum. As a term it has many uses, but in design and construction, a datum refers to a vertical measurement taken in relation to a universal elevation, such as sea level. By the way, the plural of datum is technically data, but my experience (and my research) suggests that in this context, saying “datums” is customary.Ī datum is literally a data point, defined basically as any measurement or result. One way to exercise control with vertical measurements is to work with datums and to establish a primary benchmark datum that gives a localized origin to a design or construction project’s system of vertical measurements. If you are not exercising control, then things don’t generally come together properly. Working with measurements, it is extremely important to exercise control. ![]()
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