The a per a instruments SX615 probe is the replacement probe for SX610 ph. pen r. This replacement probe is equipped with glass bulb membrane and built-in temperature sensor. It has a measurement range of -2. 00 to 16. 00 ph. and 0 to 50˚c. Its 10 mm diameter probe allows measurement in most Test tubes, making it perfect for educational use and other common aqueous solution's ph. measurement, such as hydroponics, aquaculture, pool and spas, water treatment, environmental monitoring, etc. A per a instruments has been focusing on water analysis sensors and meters over 25 years. Our products have been helping people over 25 countries have a more reliable and affordable testing experience. All of our products are CE certified.