时针显示不正确

function drawHour(hour,minute){

ctx.save();

ctx.beginPath();

var rad  = 2 * Math.PI / 12 * hour;

var mrad  = 2 * Math.PI / 12 /60 * minute; 

ctx.rotate(rad + mrad);

ctx.lineWidth = 6;

ctx.lineCap = 'round';

ctx.moveTo(0,10);

ctx.lineTo(0,-r/2);

ctx.stroke();

ctx.restore();

}

function drawMinute(minute){

ctx.save();

ctx.beginPath();

var rad = rad = 2*Math.PI/60 * minute; 

ctx.rotate(rad);

ctx.lineWidth = 3;

ctx.lineCap = 'round';

ctx.moveTo(0,10);

ctx.lineTo(0,-r + 10);

ctx.stroke();

ctx.restore();

}

drawBackground();

drawHour(4);

drawMinute(30);