var blockDelay = 5000;
var nbBlocks = 9;

var startBlockId = Math.floor(Math.random() * nbBlocks);
var currentBlock = startBlockId;

function randBlocks()
{
	var blockId;
	do
	{
		var ok = true;
		blockId = Math.floor(Math.random() * nbBlocks);
		if (currentBlock == blockId && ok)
			ok = false;
	} while (!ok);
	switchBlock(blockId);
}
function getNextBlock()
{
	var blockId = (currentBlock + 1) % nbBlocks;
	switchBlock(blockId);
}
function switchBlock(blockId)
{
	for (i = 0; i < nbBlocks; i++)
		document.getElementById("rand_service_block" + i).style.display = "none";
	document.getElementById("rand_service_block" + blockId).style.display = "block";
	currentBlock = blockId;
}