A separate test instrument, usually manufactured by Guth Industries, with its own serial number and maintenance history. It is not an "approved instrument". It holds liquid (in Ontario) alcohol standard that is poured into the simulator jar about once a week or whenever the qualified technician chooses to change the alcohol standard. The bottom jar is similar to an old glass peanut butter jar. The upper housing contains electronics and probes that go down into the liquid. The simulator holds the alcohol standard (liquid below and gas in the headspace above) at a temperature of 34 degrees C plus or minus .2 C.