Create a zabbix trapper item (float), send a value (or identical values) in range between (including) -13.94 and -13.99.
From latest data page, on a simple graph (height = 200 px), these values will not be shown.

I suppose they are drawn on a most bottom pixels line and supposedly overwritten by X axis line.
Note that values out of the range will be shown:
-14.00 shown with different Y axis scale.
-13.93 as a line above X axis;