Dimensioning convention in engineering graphics: Dimension text is generally placed above which line type for clarity and readability?

Introduction / Context:
Clear dimension placement is fundamental to legible drawings. Standard practice positions numerals consistently so fabricators and builders can read values quickly without ambiguity.

Given Data / Assumptions:

• The question refers to general drafting standards common to mechanical and architectural drawings.
• We compare four line types: dimension, extension, center, and leader.
• We assume standard Western reading conventions (left-to-right, above the dimension line).

Concept / Approach:

Dimension lines carry arrowheads (or ticks) that span the measured distance; the dimension value is centered and placed above the dimension line (or within a break in the line, depending on standard) for best readability. Extension lines project from features and do not carry text on top.

Step-by-Step Solution:

Verification / Alternative check:

Standards such as ASME Y14.5 and architectural graphics texts show dimension values on or just above the dimension line with consistent orientation (read from bottom/right in mechanical; aligned text in architectural depends on office standard).

Why Other Options Are Wrong:

Extension: supports the dimension line but is not the host for the value.

Center: indicates geometry center; not used for dimension numerals.

Leader: used for notes, surface texture, and callouts, not length/size values.

Common Pitfalls:

Placing text off-center or crossing other geometry; maintain clearances and avoid clutter.

Final Answer:

Dimension