New Generation Firmware (Series 15, Newer Series 800 and Series 400):
Menu > System > Fingerprint
Original Firmware (Series 10 and Older Series 800):
Menu > System > System
Threshold 1:1: 15 (default) > 10, minimum 5
Threshold 1:n: 35 (default) > 25, minimum 15
Sensitivity: Low / Mid (Default) / High > no need to change unless clock is not responding at all
There is an increased risk of false positive the lower the number is. When using Identify Mode (1:n) the clock will find the FIRST successful "match" in the database, not the BEST successful match
It is a simplification of logic, but imagine the setting is equal to the required points of similarity. It's pretty unlikely that a alternate person will have 35 points of similarity to another employee (default setting). As the value is lowered, the probability of a false positive increases.
On the other side of the equation, the higher the setting, the less likely false positive, at the cost of an increased false rejection. False rejections are the result of the initial fingerprint and current fingerprint being too different. This can come from a dirty lens on the reader, scratches on lens, scratches or cuts on the finger pad, especially dry or wet fingers and chemicals.
See this related article on improving fingerprint success rates: