Plot of Mass by Time The Plot of Mass by Time tab is shown below: The Plot of Mass by Time tab contains the following element: • One bivariate fit plot. This tab displays a bivariate fit plot plotting the x and y values (mass versus time, in this example) for each observation. This is a two-dimensional summary of the data from all of the columns. In this example, the progressive increase in the mass of moieties above 1000 Da shows larger moieties require more time to move through the column.