Re: why matching?
Because nearly all physical parameters have relative high spread and change with temp in silicon devices.
If you built mechanical devices you can habe high precision. There are some cases where for instance compensation of temp effect in the pendelum of a wall clock is used or paired temp effect. But in silicon nearly every thing change.
The only relative high precision effect which you could get is matching. That is because of the lithografic accuracy and homogene wafer processing.
This effect is used since 50 years for all analog circuits. We could say it is the heart of analog IC design.
It start in the 60s with the introduction of operational amplifiers. Here matching is used to reduce the effect of varying device voltage on the input related accuracy.