Lesson-specific diagram for Water and soil analysis: pH, dissolved oxygen, nitrate, and phosphorus. It visualizes the reasoning sequence tied to $\text{sample}\to\text{method}\to\text{calibration/data}\to\text{qualified conclusion}$. Text alternative: Chemical analysis requires method choice, calibration/quality control, uncertainty, context, and cautious interpretation rather than treating a sensor reading as self-explanatory. Choose a representation that matches the chemical scale and evidence; do not infer more precision or mechanism than the data support.