The most important complex factor here is how accurately it detects the LH surge and when it appears, because that determines the fertile window accurately. Some kits claim high accuracy and predict an LH jump within hours before ovulation, with results in just a few minutes. Also, having more than one pack with 5 strips gives you multiple testing periods to confirm results and pinpoint the most fertile days. Depending on the product, confusion is minimized once you follow the instructions, check the expiration date, and understand that LH readings are a key indicator of the timing of your fertile period.