What Is the Role of a “Tick Chart” in Visualizing the Difference between Quoted and Effective Spread?

A tick chart plots every executed trade price. In a thin market, a large market order will show up on the tick chart as a series of sequential trades at progressively worse prices (higher for a buy, lower for a sell).

This visual "stair-step" clearly illustrates the slippage and the widening of the effective spread beyond the quoted spread. The tick chart provides a granular, visual record of the price impact of a trade.