Double year zero calendar

The double year zero calendar it has not only one zeroth year, but two of them. The first one, 0 (alternatively 0+), is this current year 2021, and the second one, -0, is the previous year 2020. This calendar's 12.31.-0 and 1.1.0 (1.1.0+) would be the Gregorian calendar's December 24, 2020 and December 25, 2020 respectively, so all years before 0/0+ are -, and all years after -0 are +. Each year name confines to the existence of both a zero and an inverted zero, so each 10 years before 0+ is -9 to -0 (meaning the -0s), while every 10 years since 0+ is 0-9 (meaning the 0s), so the - era and + era (minus era and plus era) are complete with accurate decades and real without doubt. Each decade equals 10 years. Before the time of this post publishing, there was only a single zeroth year (0) in my year zero calendar, meaning that what is now -0 used to be -1, but I didn't wanna confuse the tenth year prior to 0+ as a new decade, so I added a second zeroth year to make the double year zero calendar. In short, the double year zero calendar was created by me because I wanted two year 0s. A new kind of year naming system made out of modifying my pre-existing year zero calendar.