LM399 is a Precision Reference chip. From this a dual polarity mirrored reference is derived using OP07 op-amps. This assembly is mounted in a miniature oven to ensure temperature stability.
Instrumentation and Measurement Circuits
The oven used Two Steel Boxes one mounted in another with Glass Wool In-between to reduce heater losses. Steel was used to ensure excellent EMI-RFI Shielding. Both the outer and internal shell was earthed.
Regulated and Filtered Supply to this assembly further ensures consistent performance over the years and in various environments and seasons.