At the request of AlexT, I implemented a new feature in Wise Clock 4, which allows the display of time lived (since birth) in different formats (years/months/days/hours/minutes/seconds, days only, hours only, minutes only).
The above photo shows the year/month/day on the top row and the hours/minutes/seconds on the bottom row.
Lifetime in Wise Clock 4 from florinc on Vimeo.
The birth date and time are read from the file message.txt on the SD card.
I was inclined to use the Time library, but I found it a little bulky for my needs and also unsuitable for dates before 1970. Then, I copied and modified the function makeTime() to convert a datetime to seconds, and I wrote my own diffTime() function to calculate the difference (in years, months, days etc) between two dates.
Alternating between display modes is done by pressing the SET (middle) button.
This code will be included in the next release of Wise Clock 4 software.