NCA-GENL Data Analysis and Visualization Practice Question
A data analyst is preparing a dashboard for an LLM inference service. The service logs per-request latency in milliseconds. The team wants a single chart that lets an on-call engineer quickly see both the typical latency and how often requests exceed the service-level objective of 500 ms. Which visualization best supports that goal?
⚠ Common exam trap
The trap here is choosing a chart that shows only central tendency and missing the tail behavior that determines SLO compliance.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A histogram of latency with a vertical marker at 500 ms
A histogram shows the latency distribution in ordered bins, so the typical range and the tail are both visible. Adding a vertical marker at 500 ms turns the chart into a threshold monitor, making SLO exceedance immediately apparent. Mean-only line charts, pie charts, and scatter plots each omit either the distribution shape or the threshold context needed for fast operational decisions.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A pie chart of requests grouped by latency bucket
Why it's wrong here
A pie chart shows proportions of a whole, but latency buckets are ordered ranges and a pie chart loses that ordering. It also makes it hard to compare the share above 500 ms against the typical range at a glance. For operational monitoring, a pie chart is a poor choice because it emphasizes composition rather than distribution and threshold exceedance.
- ✗
A time-series line chart of mean latency only
Why it's wrong here
A mean latency line chart hides the tail of the distribution. A few very slow requests can be masked by many fast ones, so the mean may stay below 500 ms even when a meaningful fraction of requests exceeds the SLO. The team needs to see both typical behavior and threshold exceedance, which the mean alone cannot provide.
- ✓
A histogram of latency with a vertical marker at 500 ms
Why this is correct
A histogram with a vertical marker at 500 ms shows the full latency distribution, including the typical peak and the tail beyond the SLO. The marker makes exceedance visually obvious, and the shape reveals whether the distribution is unimodal or heavy-tailed. This single chart supports both quick situational awareness and threshold monitoring for on-call engineers.
- ✗
A scatter plot of request size versus latency
Why it's wrong here
A scatter plot of request size versus latency explores correlation between two variables but does not summarize the overall latency distribution or highlight the 500 ms threshold. An on-call engineer would have to mentally estimate how many points lie above the line. It adds complexity without directly answering how often the SLO is exceeded.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official NVIDIA exam blueprint
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