There is other history apart from European history. I see no confirmation from Arabic, Russian or Chinese history which would certainly show a 'sudden jump' over the years which were supposedly invented.
Grep the article for "If someone had changed the calendar, wouldn't anyone else – say the Muslims? – have noticed?" -- a paragraph which ends with:
"All these areas would require an enormous amount of research either to validate or refute the theory, research that is unlikely to be undertaken by anyone not interested in rewriting the timeline."
Time moving forward. The only reason I can see for it being a wave shape is to more clearly mark each year. The years can be found at the highs and lows of the wave.
If you ignore the shape and just think of it as a long multi-line spanning timeline then it should make a little more sense.
