Feature Request: Default value property for difference method

It would be really helpful to have a default value option for the difference method. Basically, you could set the default value to some static number so the first point would not be dropped.

In my case, this would be helpful in a template I am building called "Alivewoman". Basically, its the opposite of deadman: alert when data arrives.
The stats method and difference method are perfect for this, but the first point is always dropped which is undesirable since this could be critical issue (imagine alerting when an error point is received, but dropping the first point)

I don't know how hard of a fix this would be, but I'm willing to try and learn go to add this feature in.

Thanks!

Start by locating the difference method and any tests covering its first-point behavior; the issue does not name specific files or entry points. Trace how the method handles the initial point, then add coverage showing that a configured static default keeps that point, and run the relevant test suite.

Written by the indexing model from the issue text.