<!--

function sync_month_buttons() {
	imgf = "../images/btns/bg/ice/";

	str = "";
	if (at_beginning_of_time()) { str = "_off"; }
	document.images["prev_month"].src = imgf + "prev" + str + ".gif";

	str = ""; if (at_end_of_time()) { str = "_off"; }
	document.images["next_month"].src = imgf + "next" + str + ".gif";
}


function at_beginning_of_time() {
	if (year == yearStart && month == monthStart) return 1;
	return 0;
}

function at_end_of_time() {
	if (year == yearEnd && month == monthEnd) return 1;
	return 0;
}


function sync_buttons() {
	sync_month_buttons();
}



function previous_month() { step_month(-1); }
function next_month() { step_month(1); }

function step_month(d) {

	if (d < 0) { if (year == yearStart && month == monthStart) return;}
	if (d > 0) { if (year == yearEnd && month == monthEnd) return;}

	save_month = month; save_year = year;

	month += d;
	if (month == 0) { month = 12; year--; }
	if (month == 13) { month = 1; year++; }

	if (!exist_data(sat_num)) {
		next_satellite();

		if (!satellite_found) {
			month = save_month; year = save_year;
			return;
		}
	}

	sync_month(); sync_year();

	update_display();
}


function set_month_within_range() {

	if ((year == yearStart) && (month < monthStart)) {
		out_of_range_msg(-1, "nearest"); month = monthStart; sync_month();
	}
	if ((year == yearEnd) && (month > monthEnd)) {
		out_of_range_msg(1, "nearest"); month = monthEnd; sync_month();
	}

}


// -->