You can find it in the above documentation of the DDU calcluation:
"Annual DDU consumption is calculated using the following formula: <# of discovered certificates> x <24 / certificate check interval (hours)> x 365 x 0.001. e.g., A single certificate checked every 8 hours will consume ~1.1 (1 x (24/8) x 365 x 0.001) DDUs per year2
There are two ways of monitoring: via oneagent or via activegate based on the configuration information.
If you use the cert infromation collection via oneagnet you will / can use the the inculded metrics per host units. https://www.dynatrace.com/support/help/shortlink/metric-cost-calculation#metrics-per-host-unit
In this case it will be only reported DDU until the included metrics DDU.
If you use the cert infromation collection via active gate the DDU will be deducted immadiately and will be consumed DDU.
Funny but I also discovered this extension today and my fisrt test was the check of the DDU consumption.😉
I think it is very useful for the organizations, howerver the big cert providers can send notification for cert expirations.