Blueprints, Schematics, and Layout
Reading the drawing set
Orthographic projection gives front, top, and right-side views. In third-angle projection (US practice) the top view sits above the front view and the right-side view sits to the right; the truncated-cone symbol in the title block identifies the convention. First-angle reverses the placement. Learn the line conventions: visible (solid), hidden (short dashes), center (long-short), phantom, break, and section hatching.
The title block carries part number, scale, material, and revision level; revision clouds with triangles flag changes. Dimensions are authoritative - never scale a drawing. Tolerances may be general (unless otherwise specified) or local. GD&T feature control frames govern form (flatness, straightness), orientation (perpendicularity, parallelism), location (position), and runout, often at maximum material condition.
Schematics and P&IDs
P&IDs show process flow with instrument bubbles whose tag letters define function (FT = flow transmitter, PSH = pressure switch high). Line types separate major process, utility, instrument air, and electrical. Isometrics give pipe routing with coordinates and weld numbers; elevations and plot plans tie equipment to site datums.
Traps
Reading first-angle as third-angle; ignoring a not-to-scale note; missing the latest revision; treating a reference dimension shown in parentheses as a tolerance; confusing nominal pipe size with actual outside diameter; stacking dimensions from feature to feature instead of from a datum.
Rule of thumb
Establish one datum (a machined surface, a centerline, or a survey point) and take every layout dimension from it. Never chain dimensions along a row of holes.