A column asking whether a feature was present appears to need only yes and no. In practice, a blank may mean the observer forgot, could not see, or never attempted the check. Those situations should not silently become confirmed negative observations.
Define the question and possible states
For an invented plant notebook, use a precise question such as “Was an open flower visible from the stated viewing position?” Decide how to record yes, no, and not checked. If an obstructed view matters, document how that situation is represented.
The categories are a design choice for this example, not a universal biological protocol. An established project may require a different scheme. Follow its definitions when contributing to it.
Count only what the question supports
Imagine ten records: six yes, two no, and two not checked. Eight records contain an attempted answer. Reporting six out of ten and six out of eight describes different denominators, so label whichever calculation you use.
Do not rewrite the unknown entries merely to make a chart complete. Preserve the original state and explain any later correction. A well-defined negative answer contains information; an unexplained blank contains uncertainty. Keeping them distinct makes a simple observation table more useful when it is eventually summarised.