What is the difference in function between a brake metering valve and a brake proportioning valve?

1. The metering valve controls parking brake tension; the proportioning valve controls front brakes
2. The metering valve delays front disc brake application until rear drum shoes make contact; the proportioning valve limits hydraulic pressure to the rear brakes during hard stops
3. The metering valve controls vacuum flow; the proportioning valve controls ABS electronics
4. The metering valve bypasses the master cylinder; the proportioning valve increases overall fluid volume