In this part we will explore the third indicator that I use which helps us in understanding the dynamics that happens in the Limit order-book before large moves, in a way this is one those “predictive” indicators as it signals oncoming volatility a few minutes before it actually does – The Average Bid-Ask Spread.

In the slack room, I call it SOS – No not “Save our Ship” but “Spikes on Spread” – Which indeed is an SOS signal if you have any positions on, as it signals one to be alert.

Before we get to the mechanics of this indicator, one needs to have a basic understanding of how the Limit Order book (LOB) works.

So if you look at the L2 market depth, this is how it would typically look at a given moment (Graphically i.e.)

Now let’s see what happens when a Market Order hits the book. In this example a Market Buy Order hits the book.

The contracts marked in Yellow are the one which are consumed by the Market Order. Now do compare the spread in the two illustrations. In the first one we have a spread of 1 and in the second, because of the market order coming in the spreads doubles to 2. Now let’s see what happens next.

As you can see in the above illustration, the limit orders (Bids) come in to fill the spread. This Expansion-Contraction of spread due to market orders coming in can happen and can be observed over different timeframes. But the concept remains the same.

Microstructure academicians also call this the Liquidity Cycle or more specifically the Make – Take Phases

Typically you have shorter “Take Phases” and longer “Make Phases”, which fits in with the fact that we would typically have lesser market orders compared to limit orders.

With theory covered now let’s move to practice.

Look at the NIFTY Futures 1 minute time frame chart (Date – 8th May’18)

On the top pane is NIFTY Futures Price, the second pane has Average Bid-ask spread as a Histogram aggregated for each minute. On the Second pane is a 5 minute (Orange) over 45 minute (Grey) SMA of the Spread, the last pane has Volume rate which we’ve looked at already in part 1 of this series.

If you notice the spread for NIFTY Futures oscillates in a range of 0 to 2.

So how do we use this indicator?

Observe the spread from 12:05 to 12:45 – If you see the price has largely been range bound but the spread moved from the upper band to the lower band – Remember the concept of “Take Phase”?

My conjecture is this is a period where liquidity takers are sort of sweeping the book, the price remains range bound up till the point where adequate liquidity exists, the moment there is an imbalance we see large moves or volatility come in, and as these initial bursts come in, perhaps herd and threshold behaviour takes over causing extensions of these moves.

Since this indicator is like an oscillator with a fairly defined range – it’s easy to spot deviations and be prepared for an upcoming move, however one must remember this indicator does not predict direction all that it does it predict volatility.

As of now I am still testing and collecting data to do back-tests on this indicator, so I do not have any statistics to support my claim, but people in the slack group know – how often I call out an ‘SOS’ and how accurate or inaccurate it turns out to be.

The usual disclaimer applies to this indicator as well – this indicator is to be used within the context of the market structure and in combination with other indicators discussed in this series.

Update - Another screen shot of NIFTY FUT 10th of May'18