Milestone charts (used to highlight key checkpoints in a schedule) were introduced historically around the year 1930.

Introduction / Context:
Milestone charts abstract a schedule into key events or deliverables. This question probes knowledge of the historical evolution of early scheduling tools relative to the Gantt chart era.

Given Data / Assumptions:

• We must choose the approximate year of milestone chart origin.
• Choices span 1910–1950.

Concept / Approach:
Gantt charts were popularized in the 1910s for depicting activities over time. As scheduling practice matured, milestone-centric views appeared to emphasize checkpoints, approvals, or phase gates—commonly referenced to the early 20th century timeline, around 1930, in classical project management texts.

Step-by-Step Solution:
1) Set context: Gantt (1910s) precedes milestone abstraction.2) Milestone emphasis gained traction in the subsequent decades.3) Historical consensus often cites 1930 for the milestone chart concept.

Verification / Alternative check:
Comparing multiple project management histories shows milestones emerging after early Gantt adoption and before mid-century network methods, aligning with 1930 better than earlier or much later dates.

Why Other Options Are Wrong:

• 1910/1920: Too close to early Gantt adoption; milestone formalization was later.
• 1940/1950: Too late given already widespread use of milestone tracking by then.

Common Pitfalls:

• Assuming milestones originated simultaneously with Gantt bars.
• Confusing the formalization of milestones with later network techniques.

Final Answer:
1930.