Another tool used to measure specific gravity is an
optical refractometer like that shown in Figure 5-36.
This tool is also used to test engine coolant freeze
protection. Newer models may also include a scale
for measuring the concentration of urea in diesel exhaust
fluid (DEF), as will be explained in Chapter 14.
A drop of electrolyte is placed on a glass window and
the specific gravity is shown when viewed through the
eyepiece. Figure 5-37 indicates a specific gravity of
1.275 for this example.