for (var i = 0; i < canvas.width; i += 25) {
context.beginPath();
context.moveTo(i, 0);
context.lineTo(i, canvas.height);
context.stroke();
}
for (var i = 0; i < canvas.height; i += 25) {
context.beginPath();
context.moveTo(0, i);
context.lineTo(canvas.width, i);
context.stroke();
}