Iso week

here is a method I use:

using Toybox.Time.Gregorian as Date;



var now = Time.now();
		var date = Date.info(now, Time.FORMAT_LONG);
		var today = Date.info(now, Time.FORMAT_SHORT); 
		var Wnum = iso_week_number(today.year, today.month, today.day);
		
		
function iso_week_number(year, month, day){
    	var first_day_of_year = julian_day(year, 1, 1);
    	var given_day_of_year = julian_day(year, month, day);
    	var day_of_week = (first_day_of_year + 3) % 7; 
    	var week_of_year = (given_day_of_year - first_day_of_year + day_of_week + 4) / 7;
    	if (week_of_year == 53) {
			if (day_of_week == 6) {
            	return week_of_year;
        	}else if (day_of_week == 5 && is_leap_year(year)) {
            	return week_of_year;
        	} else {
            	return 1;
        	}
    	}
    	else if (week_of_year == 0) {
       		first_day_of_year = julian_day(year - 1, 1, 1);
        	day_of_week = (first_day_of_year + 3) % 7;
			return (given_day_of_year - first_day_of_year + day_of_week + 4) / 7;
    	}
    	else {
        return week_of_year;
    	}
	}
	
	
	private function julian_day(year, month, day)
	{
    	var a = (14 - month) / 12;
    	var y = (year + 4800 - a);
    	var m = (month + 12 * a - 3);
    	return day + ((153 * m + 2) / 5) + (365 * y) + (y / 4) - (y / 100) + (y / 400) - 32045;
	}
	
	
	function is_leap_year(year){
    	if (year % 4 != 0) {
        	return false;
   		 }	else if (year % 100 != 0) {
        	return true;
    	}else if (year % 400 == 0) {
        return true;
    	}
		return false;
	}

Wow, it is simpler than I expected.

Thank you very much! I really think this should be part of the official library tough.

lol pretty sure you can fin simpler method but it is what I use. I do agree with you.

I composed such a code.
Maybe this is not entirely accurate, but it seems to work.

var now = Cal.info(Time.now(), Time.FORMAT_SHORT);
            week = {
                :year   => now.year,
                :month  => 1,
                :day    => 1,
                :hour   => 0,
            };
            week = Time.Gregorian.moment(week);
            // день недели 1-го января
            var jan1 = Cal.info(week, Time.FORMAT_SHORT).day_of_week;
            week = week.value(); // start year
            if (jan1==1) {
                jan1=7;
            } else {
                jan1-=1;
            }
            if (jan1>4) {
                jan1=8-jan1;
                week += jan1*86400; // start 1st mon of year
            } else {
                jan1=3-jan1;
                week -= jan1*86400; // start 1st mon of year
            }

            week = Time.now().value()-week;
            if (week>=0) {
                week = (1 + week/604800).toNumber();
            } else {
                week = 0;
            }

Thank you very much for your answer too. Where did you get the "algorithm" ? You built yourself? Are you using it on any watchface?

I built this "algorithm" yourself and use it in WF AdjustableAnalogRebith.

Thanks