The whole statement in the article is utter nonsense: "In that year, over 250 bishops came together at Nicaea to discuss the increasing problems concerning the date of Eastern. At this meting, they decided that from that point on, March 21 would be the vernal equinoctial point, which would mean that the calendar would have the same pace as the solar year. The last dodecahedrons descend from the fourth century AD."

That in 325 AD the vernal equinox fell on 21 March in the Julian Calendar was just a matter of fact. No one except of a few experts cared for more than a thousand years, that the calendar date of the vernal equinox gradually changed, amounting to 1 day aprox. every 128 years.

The "classical" way to "measure" the date of the equinox is by using a so-called gnomon, a vertical stick. At the date of the spring or autumn equinox, the tip of its shadow over the day results in a straight line. Here is an illustration and a longer explanation: https://earthsky.org/human-world/equinox-shadows-trace-a-str...

Looks like typos to me.