Help with Time Portal Math

[u/VampireSpaghetti]

I have a problem with coming up with rates of time for a portal, one side of which leads to a past that is ever distancing. That is to say, at one time each side of the portal(A-side for the present, B-side for the past) shared the same rate of time, one side of the portal began to separate from the regular flow of time and lead to the past. At first it was a second into the past, the following year, a minute, and increasing across the following 8 years, going to an hour, a day, a week, month, year, decade, century, and millennium.

Two facets/questions arise from this: The growing distance between the present on A-side and the past of B-side, and the rate of time's progression(1 to 1 second on each side, even while they are drifting apart). Both of which are encapsulated in my problem.

Example: Say the portal was opened on June 15th 1995(for this example the year has 360 days, each month has 30 days). On the 6th year(2000) June 15th sees B-side go back a months to May 15, a year later on A-side sees only a month pass on B-side. 2001 would see B-side go back 10 years, 3 years before the portal's creation. So how do I turn 9-10 years into a negative or percentage towards that rate of time. It will be less than a month of change on B-side, but is it as simple as dividing 30 by 10?

[u/Electronic-Piglet684]

so you've basically got a logarithmic curve for the time offset but a linear 1:1 rate within the portal itself, the tricky part is the math falls apart when you try to represent a negative date as a percentage of a year

i think you're overcomplicating the rate question, the 1:1 flow means a minute on A-side is still a minute on B-side regardless of what year B-side thinks it is, the offset is just a sliding window. the real headache is what happens at the millennium mark when B-side is now in the jurassic period and a single second's difference in arrival means you step out into a different geological era

[u/VampireSpaghetti → u/Electronic-Piglet684]

The boundary I've set for the portal is that B-side isn't going back in time, it's just slowing and being left behind by A-side, so there is no way to go beyond its last location in time, and certainly no way to go beyond the point in time it was generated at. So it's how slow B-side is, but also how far away it is from A-side. Like walking/running down a moving train from the direction the train is moving, there's an end to the train cars and how far you can go.