Basic numbers

What Are Basic Dimensions?


Basic dimensions describe the theoretically exact location, orientation, size, or profile of a feature or datum target. Because basic dimensions are theoretically perfect dimensions, there are no tolerances associated with them. A basic dimension is noted as a dimension with a box around it and must mathematically relate back to the Datum Features. In ISO standards, basic dimensions are called TEDs – Theoretically Exact Dimensions.

Because basic dimensions refer to theoretically perfect positions, when chain dimensioning basic dimensions, there is no tolerance accumulation.

Basic dimensions must always include a geometric control to ensure that there are no dimensions with a zero tolerance. Therefore, a basic dimension can be thought of as a nominal dimension where the geometric tolerance sets the tolerance range. Basic dimensions are always used to locate a feature using Position.

To better understand basic dimensions, let’s look at an example. Figure 1, which is discussed in the video, shows a part containing a pattern of four cylindrical holes. Basic dimensions of 15 and 30 are used to locate the true position of the holes from Datum Features B and C. We know that these are basic (thus, perfect) dimensions because this is indicated by the dimensions having a box around them. The geometric tolerance for the holes, shown in the feature control frame at the upper right hand of the drawing, defines the tolerances for both the position and size for the pattern of holes

https://www.gdandtbasics.com/reporting-basic-dimensions/
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What Are Basic Dimensions?


Basic dimensions describe the theoretically exact location, orientation, size, or profile of a feature or datum target. Because basic dimensions are theoretically perfect dimensions, there are no tolerances associated with them. A basic dimension is noted as a dimension with a box around it and must mathematically relate back to the Datum Features. In ISO standards, basic dimensions are called TEDs – Theoretically Exact Dimensions.

Because basic dimensions refer to theoretically perfect positions, when chain dimensioning basic dimensions, there is no tolerance accumulation.

Basic dimensions must always include a geometric control to ensure that there are no dimensions with a zero tolerance. Therefore, a basic dimension can be thought of as a nominal dimension where the geometric tolerance sets the tolerance range. Basic dimensions are always used to locate a feature using Position.

To better understand basic dimensions, let’s look at an example. Figure 1, which is discussed in the video, shows a part containing a pattern of four cylindrical holes. Basic dimensions of 15 and 30 are used to locate the true position of the holes from Datum Features B and C. We know that these are basic (thus, perfect) dimensions because this is indicated by the dimensions having a box around them. The geometric tolerance for the holes, shown in the feature control frame at the upper right hand of the drawing, defines the tolerances for both the position and size for the pattern of holes

https://www.gdandtbasics.com/reporting-basic-dimensions/
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Thank you, just as I thought also. Information much appreciated.