For an automotive application, our provider and us had to find a way to have a very accurate RTC and of course with a very low cost.
The solutions we have studied were :
- high accuracy crystal (few ppm)
- temperature compensated oscillators
- software temperature correction.

We have designed this last solution because it's cost effective and very reliable.

By measuring the temperature near the crystal and according to datasheet, the readed temperature was compensated. The purpose is to have a more linear curve than the crystal was able to provide. Thus, we could use low cost crystals and have a very high accuracy.

Regards
Stephane