I was looking at an order book yesterday and saw orders which I haven't seen before. Normally an order in the order book consists of the total volume, the price and how many sellers/buyers are ready to buy/sell for this price.
1722 is the volume, 3 is the amount of buyers and 13.80 is the price.
Now to the question: The order which I found were strange, had a volume, a price, but no amount of buyers/sellers. The looked like 1722(-) 13.80. What also was very strange was that there was always for example a volume of 4000 on the byers site and the exactly same volume on the sellers site, but they did never hit each other, there was always a spread. A third strange thing was that these orders were updated nearly every 5 seconds, so I think these orders must come from a computer system and not from a human being.
Can someone please explain to me what these orders were? I would also appreciate some background information.
Thank you in advance.