[ben_w]

The IMUs that existed on aircraft before the invention of GPS have been superseded by the ones which actually are in your phone, in much the same way and for much the same reason that a $20 Casio F-91w keeps better time than a fancy Rolex that costs more than a house in California: electronics are cheaper and better than mechanical systems.

We have, naturally, also made better IMUs for places where it matters, ones which won't fit in your phone.

The question is therefore not suited to "aircraft grade, yes or no?", it's "how expensive is the cheapest IMU that's good enough for the specific need?" which in this case itself depends on how many stops is desired.

[wkat4242]

Actually that F91W does not keep very good time.

There pretty excellent if you keep them on a shelf bit if you run around outside in the hot and cold (you know, like people use a watch) they'll deviate quickly. Because they don't have a temperature controlled (or even compensated) oscillator. A real TXCO (basically putting the crystal inside a temp calibrated oven) is not feasible on a watch battery but compensation sure would be.

[ben_w]

I picked it not because it's good, but to illustrate the cheapest digital is still better than any analog mechanism that money can buy.

[wkat4242]

Ah ok,I didn't realize analog watches were that bad.

[minetest2048]

> A real TXCO (basically putting the crystal inside a temp calibrated oven) is not feasible on a watch battery but compensation sure would be.

Nitpick: You're thinking about OCXO for crystals inside an oven, TCXOs are temperature compensated crystal oscillators