What counts as a weak key
The browser aggregates correct attempts, errors, and timing for letters and digits. Spaces and punctuation reset the latency chain so a pause at a word boundary is not blamed on the next letter.
Keys below the minimum sample threshold are not ranked. Physical-keyboard and touch results stay separate because the movement and timing conditions are incompatible.
How a drill is assembled
A local index finds common words containing the selected letters and useful pairs such as er, re, th, or st. Difficulty considers word length and less common key demands.
The generator places selected words into original readable sentence frames. It progresses from familiar words toward longer forms and punctuation instead of producing an unstructured word salad.
When before-and-after is shown
An adaptive result compares earlier weak-key accuracy with the practice session only when both sides contain enough relevant attempts. If the evidence is thin, KeyVelocity says that it is collecting comparison data.
A positive change in one session is a practice signal, not a guaranteed permanent improvement. Retest in a comparable standard mode to see whether the gain transfers.