1.4 The Y14.5-2018 Senior Exam and What Changed from 2009

ASME GDTP Senior Level Exam

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1 Introduction & Exam Overview

1.1 Current Exam Facts 1.2 Senior Level vs Technologist and Y14.5 Revisions 1.3 How to Use This Guide and Study Strategy 1.4 The Y14.5-2018 Senior Exam and What Changed from 2009

2 Dimensioning and Symbology

2.1 Y14.5 Dimensioning Rules, Limits, and Fits 2.2 Basic Dimensions and Their Role 2.3 Feature Control Frame Structure and Reading 2.4 GD&T Symbols, Modifiers, and Communication 2.5 Screw Threads, Gears, and Splines 2.6 Angular Surfaces, Tapers, Radii, and Special Tolerance Cases

3 Datum Referencing I: Selection and Precedence

3.1 Functional Datum Feature Selection 3.2 Datum Precedence and Degrees of Freedom 3.3 Datum Targets 3.4 Datum Feature Simulators

4 Datum Referencing II: Modifiers and Shift

4.1 Multiple Datum Features and Datum Reference Frames 4.2 RMB, MMB, and LMB on Datum Features 4.3 Datum Shift Behavior 4.4 Planar vs Datum Feature of Size

5 Datum Referencing III: Setup and Calculations

5.1 Inclined and Translated Datum Features 5.2 Inspection Setup and Datum Establishment 5.3 Datum Calculation Walkthrough 5.4 Customized Datum Reference Frames and Rotational Constraint 5.5 Free State, Restrained Condition, and Nonrigid Parts

6 Form Controls

6.1 Flatness and Straightness 6.2 Circularity and Cylindricity 6.3 Rule #1, Form, and Size

7 Orientation Controls

7.1 Parallelism, Perpendicularity, and Angularity 7.2 Orientation Zones and Material Modifiers 7.3 Avoiding Unnecessary Orientation and Over-Control

8 Location I: Position and Boundaries

8.1 Position Tolerancing and True Position 8.2 Virtual and Resultant Condition 8.3 Bonus Tolerance at MMC and LMC

9 Location II: Application and Modifiers

9.1 Selecting MMC, LMC, and RFS by Function 9.2 Fixed and Floating Fastener Formulas 9.3 Projected Tolerance Zones 9.4 Coordinate Conversion and Appendix B Position Calculations

10 Location III: Patterns and Allocation

10.1 Composite Position Tolerancing 10.2 Patterns, Simultaneous Requirements, and Multiple Segments 10.3 Slots, Tabs, and Tolerance Allocation 10.4 Coaxial Feature Controls, Concentricity, and Symmetry

11 Profile I: Fundamentals and Strategy

11.1 Profile of Line and Surface 11.2 Defining the True Profile 11.3 Datum-Referenced Profile Strategy 11.4 Equal and Unequal Disposition

12 Profile II: Scope and Verification

12.1 All-Around, All-Over, and Limited Scope 12.2 Composite Profile and Coplanarity 12.3 Castings, Weldments, Sheet Metal, and CMM Evaluation 12.4 Combined Controls and Profile as a Refinement

13 Runout Controls

13.1 Circular and Total Runout 13.2 Datum-Axis Simulation and Rotating Parts 13.3 Runout vs Position, Profile, and Form

14 Exam Strategy and Calculations

14.1 Virtual/Resultant Condition and Bonus Formulas 14.2 Datum Shift and Worst-Case Boundary Calculations 14.3 Functional Gaging and Verification 14.4 Test-Day Tactics, Common Traps, and Review

1.4 The Y14.5-2018 Senior Exam and What Changed from 2009

Key Takeaways Explain This Topic AI

The 2018 Senior blueprint is organized by standard section number — 10% Sections 3-6, 30% Section 7 (Datum Reference Frames), 5% Section 8, 5% Section 9, 25% Section 10 (Position), 20% Section 11 (Profile), 5% Section 12 (Runout) — with the same weights as 2009 but a 74% overall pass mark.

Y14.5-2018 deleted concentricity and symmetry; a 2018 candidate controls those relationships with position, runout, or profile instead.

2018 renamed 2009's "datum feature simulator (theoretical)" back to "true geometric counterpart" and renamed "multiple datum features" to "common datum features".

2018 replaced the 2009 candidate-datum-set method for rocking datum features with a single default stabilized solution that minimizes separation between the feature and its true geometric counterpart.

The dynamic profile modifier is the headline new 2018 symbol: it lets profile control form without also controlling size.

Last updated: August 2026

The Y14.5-2018 Senior Exam and What Changed from 2009

Quick Answer: The 2018 Senior exam uses the same seven weights as 2009 but labels them by standard section number and passes at 74% instead of 78%. The technical deltas that matter are: concentricity and symmetry deleted, dynamic profile added, "true geometric counterpart" restored, "common datum features" renamed, and a single default stabilization rule replacing the candidate datum set.

ASME runs the 2009 and 2018 Senior exams side by side . You buy one or the other, and the certificate you receive names the revision you passed. Nothing about passing 2009 grants 2018, and nothing about passing 2018 grants 2009. Section 1.2 covered how to choose; this section maps the 2018 blueprint and isolates the technical delta so that a candidate trained on 2009 material knows exactly what extra ground to cover — and so that a candidate sitting 2009 knows which 2018-only concepts to ignore .

The 2018 Senior blueprint

The 2018 outline is organized by standard section number rather than by topic name. The weights are identical to 2009:

Section(s) Topic Weight ~Questions of 150
3-6 Definitions, Rules, Tolerancing, Symbology 10% 15
7 Datum Reference Frames 30% 45
8 Form 5% 8
9 Orientation 5% 8
10 Position 25% 37
11 Profile 20% 30
12 Runout 5% 8

Pass requires 74% overall and at least 50% in each section . The 2009 exam requires 78% overall with the same 50% floor. Both are 150 scored multiple-choice questions with a maximum duration of six hours, both are closed book, and both require knowledge of Nonmandatory Appendix B, Formulas for Positional Tolerancing .

Notice the naming shift. Where 2009 says "Location," 2018 says " Position " — because 2018 deleted the other two location controls (concentricity and symmetry) and Section 10 now contains position alone. Where 2009 says "Datum Referencing," 2018 says " Datum Reference Frames ." Where 2009 says "Scope, General Dimensioning, and Symbology," 2018 says "Sections 3 through 6 (Definitions, Rules, Tolerancing, Symbology)." Same ground, different labels.

Delta 1: Concentricity and symmetry are gone

This is the largest single change. Y14.5-2009 clauses on concentricity (◎) and symmetry (⌯) controlled the median points of diametrically opposed elements or opposed surfaces. Both were RFS-only, both were extremely expensive to verify, and both were widely misapplied where position or runout was the correct control.

Y14.5-2018 deleted both symbols . On a 2018 drawing you achieve the same design intent with:

Position on a feature of size when you care about the derived median plane or axis location — and you may use MMC, which concentricity never allowed.

Runout when you care about the surface as it rotates about a datum axis.

Profile when you care about the surface itself relative to a datum reference frame.

For the 2009 exam these two controls are live BoK content (see Section 10.4). For the 2018 exam, a question naming concentricity is testing whether you know it no longer exists.

Delta 2: Dynamic profile

The dynamic profile modifier is the marquee new 2018 symbol. Ordinary profile applied to a non-planar feature controls size, form, orientation, and location together, because the two boundary offsets from the true profile are fixed. The dynamic modifier makes the offset between the boundaries stay constant while the boundaries themselves float , so profile controls form without also constraining size . On a hole, dynamic profile with no datum references behaves like cylindricity; on a complex contour it does what no other single symbol could previously do. Expect at least one 2018 Profile question on it.

Delta 3: Terminology reversals

Two terms flipped between revisions, and the exam writers know it:

2009 term 2018 term
Datum feature simulator (theoretical) True geometric counterpart
Multiple datum features Common datum features

The concepts did not change; the words did. "True geometric counterpart" had existed in 1994, disappeared as a defined term in 2009, and returned in 2018. If you learned the 2009 vocabulary, you must be able to read the 2018 vocabulary and vice versa.

Delta 4: Default stabilization replaces the candidate datum set

When a primary datum feature is convex and rocks on its simulator — or when a datum feature of size referenced RMB can settle in more than one way — 2009 permitted a candidate datum set : a family of permissible datums, and the part passed if any member of the set worked. 2018 replaces this with a single default stabilized solution : the part is adjusted to the one solution that minimizes the separation between the datum feature and its true geometric counterpart. One answer, not a search. This tightens inspection repeatability and it is a favorite 2018 Datum Reference Frames question.

Delta 5: Smaller items on the 2018 Senior body of knowledge

The published 2018 Senior body of knowledge also names a few items the 2009 list does not:

Dimensions related to an origin (the origin symbol, which fixes which surface is the measurement origin in a plus-minus dimension).

Average diameter listed under Form, for nonrigid parts.

Profile of a line as a refinement of profile of a surface, called out explicitly.

Tolerance zone shape (2018) where 2009 says "definition of the tolerance zone."

The from-to symbol for designating the extent of a requirement between two points.

What transfers untouched

Do not over-rotate on the delta list. Degrees of freedom, datum precedence, datum targets, MMB/LMB/RMB, datum shift, Rule #1, all four form controls, all three orientation controls, position and its boundaries, bonus tolerance, projected tolerance zones, composite frames, profile scope and disposition, and both runout controls behave the same way in both revisions. The arithmetic in Chapters 8, 9, and 14 of this guide is revision-neutral. Roughly nine-tenths of your preparation serves either exam; budget a focused delta review for the last tenth.