How does CB Advanced Digital opk work?

I know wondfos just measure your LH each day, but how does CB with the solid and flashing smiley work?
​Does it measure estrogen and LH in relation to the day before? Or just measuring the levels in each day's urine?
​For example, if I get a positive on wondfo, will CB show a solid peak smiley if it had never shown a flashing smiley?