Slow but sure means slow or incremental but yielding steady dependable progress, which is what he was doing as he edged across the floor.
Context: With slow but certain movements, he edged across the finely-fitted hardwood floor towards the place of fire.
Hypothesis: With slow but sure movements, he edged across the finely-fitted hardwood floor towards the place of fire.

Is the hypothesis incorrect? (Yes, no, or unknown)?