A Runic calendar (also Rune staff or Runic Almanac) is a perpetual calendar, variants of which have been used in Northern Europe until the 19th century.

The calendar is based on the 19-year-long Metonic cycle, correlating the Sun and the Moon. Runic calendars were written on parchment or carved onto staves of wood, bone, or horn. The oldest one known, and the only one from the Middle Ages, is the Nyköping staff from Sweden, believed to date from the 13th century. Most of the several thousand which survive are wooden calendars dating from the 16th and the 17th centuries. During the 18th century, the Runic calendars had a renaissance, and around 1800, such calendars were made in the form of tobacco boxes in brass. On one line, 52 weeks of 7 days were laid out using 52 repetitions of the first seven runes of the Younger Futhark. The runes corresponding to each weekday varied from year to year.

On another, many of the days were marked with one of 19 symbols representing the 19 Golden numbers, the years of the Metonic cycle. In early calendars, each of the 19 years in the cycle was represented by a rune; the first 16 were the 16 runes of the Younger Futhark, plus special runes for the remaining three years: Arlaug (Golden Number 17), Tvimadur (Golden Number 18), and Belgthor (Golden Number 19). The new moon would fall on that day during that year of the cycle. For example, in the 18th year of the cycle, the new moons would fall on all the dates marked with Tvimadur, the symbol for year 18. Later calendars used Pentadic numerals for the values 1–19. https://en.wikipedia.org/wiki/Runic_calendar

The Elder Futhark names this rune Hagalaz; To the Icelanders and their Younger Futhark, it is Hagal. The Anglo Saxon and West Germanic folk call this rune Haegl. To Guido von List – he too named this rune Hagal. The rune poems sing of this rune- the destructive hail that rains down upon us. Yet this rune has the power to heal the body and calm the mind. It is a health promoting and holy rune. Some people form the rune with two upright staves joined by a diagonal one. This is the way the rune is drawn in the Ar Kan Rune Lag – the rune system of Woden’s Folk. When performing collective rituals this is the rune we use. However I also use this rune in its alternative form – three crossed lines forming a six pointed star. When I look at this rune I see reflections of life and death, a rune binding of male and female and compulsion to duty.

All the rune poems equate Hagal with the hailstone. Hail is the whitest of grains; Hail is the coldest of grains. The Old English word Haegl, Danish Hagl and the German Hagel all mean ‘hailstone’. But this is just one aspect of the rune. I prefer to call this rune ‘Hail’ rather than Hagal (pronouncing the g). If we take a quick look at some old Anglo Saxon words we find that ‘g’ was pronounced as a ‘y’ (as in these examples - geollu – yellow, geol – Yule, ge –you). This means our Hagal rune could be pronounced as Hayal, so it would be the same as Hail. The word Hayal is important as this connects the rune to the sacred mountain http://volkisch-runes.blogspot.com/p/hagal.html