Underlying datetime values in macOS Numbers

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Level 2

164 points

Underlying datetime values in macOS Numbers

In macOS Numbers, when I create a Scatter Plot with Dates along the X-Axis , and then display a Trendline (along with checking "Show Equation"), what numeric x-values is Numbers using for the dates?

I would assume that Numbers uses a Linux Epoch Timestamp internally for each date, but after some trial-and-error using the quadratic formula, and can't demonstrate this. I believe the quadratic formula may be super-sensitive to rounding errors in this case.

I *think* the following is a link to a simple Numbers file demonstrating this: Sample with Trendline and Dates

iMac (2017 – 2020)

Posted on Dec 27, 2024 11:10 AM

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Answer 1

Top-ranking reply

6x6

Level 6

19,305 points

Dec 27, 2024 5:33 PM in response to Badunit

Hello Badunit,

After some testing, I confirm that the dates used for the regression are represented as the number of seconds since 01/01/2001.

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Answer 2

MJ Author

Level 2

164 points

Dec 28, 2024 11:03 AM in response to MJ

I guess I am way behind the curve...billions of Apple devices encode dates with a reference at 1/1/2001...

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Answer 3

Badunit

Level 7

30,366 points

Dec 27, 2024 5:27 PM in response to MJ

Interesting question. I don't know what it is doing exactly but here is an observation:

If column A (X data) is dates starting at 1/1/2001 and increasing by D days per row and column B (Y data) is numbers starting at 0 and increasing by D per row, the intercept on the scatter chart linear trend line is 0. The slope of 1.157E-5 (which appears to be 1.15740740740741E-5) indicates that a day is equivalent to 24*60*60 = 86,400 seconds.

A formula can probably be deduced from this and a few other observations.

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