To remember about when I did something／いつ頃やったかを忘れないために

I think that I have invented the way to remember on what day something is done in a simple fashion. Taking today's date, April (the fourth month) 19th year 2021 Monday（月曜日） for example, it is written as "041X_21（月）." Since we are not likely to keep alive for more than one hundred years, I think that there is no need to make it clear what numerical indices over the orders for 10 to 99 of year's number the date is in. In addition, as to the date, I do not think that since almost always it is not necessary to make it clear exactly what date it is, I write only the number of the order of 10, and hide that of the order of 1 and write “X” in that place. Although I do not mean to compensate for that simplified system, I put the Chinese character of the name for expressing what day of the week it is in parentheses.

　何かをした日を覚えておくためのシンプルな方法を開発したつもりでいます。具体例として、本日、2021年4月19日・月曜日に関しては、「041X_21
（月）」とします。我々が100年を超えて生きることはそうそうないので、私は、その日が西暦何年であるかを示す数字の10の位の上は略すことにしました。また、日にちの数も、10の位だけ明示し、1の位は X とします。その代わりと言う訳ではありませんが、最後に曜日を示す漢字一字をカッコに入れて示します。