[yongkimleng]

For non critical applications with decent margins of error, the LM19 is pretty sufficient and pre-calibrated. Your only problem may be insulating it unless you can find the metal-can package of it so you can dip its "head" into the fluid, or drill a hole at the side of the fluid container to place it, ensuring that no fluid touches the electrical pins. Hopefully your fluid isn't charged too.. dunno if the metal case is grounded or not.