CFF thresholds differ by maximum 30 Hz between participants. 95% prediction interval spans 21 Hz. Three measurement methods highly correlated (r=0.68-0.93). No mean CFF difference between males and females. 80% of variance from between-individual differences. 10% variance from within-individual changes over three sessions. CFF stable across sessions in males (P>0.05). CFF significantly increases across sessions in females (P<0.001 for two methods). Females show 1.6 Hz average increase vs 0.4 Hz in males. Variation comparable to differences between species in different niches. CFF measured reliably with low-cost LED device in under 10 minutes. Ascending method prone to outliers. Shortened constant stimuli method precise and fast. All participants aged 18-35 with normal vision. Thresholds normally distributed except two low outliers. Session positively correlates with CFF rise in females.