The R.B. Annis Model 25 Magnetic Field Indicator is a vintage gauss meter manufactured in the United States. This device is designed to measure magnetic fields and is part of the aviation parts and accessories category. The brand, R.B. Annis, is known for producing high-quality instruments, making this magnetic field indicator a reliable tool for aviation and other applications that require precise measurements of magnetic fields. Its vintage design may add collectible value for enthusiasts of aviation parts and equipment.