I built HillFactor as a focused Naismith pacing data field for hill walking, hiking and trail running. It shows your cumulative Naismith factor, compares it with a target you choose, and makes the result explicit as AHEAD, ON TARGET or BEHIND with a signed time delta.
A lower factor means faster progress. HillFactor works offline, needs no account, and only writes its optional factor series into your saved FIT activity. It supports a wide range of current Garmin devices and is available in English and Spanish.
HillFactor is a pacing aid, not navigation or a guaranteed finish-time predictor. Elevation quality depends on the watch and the activity.
I am the developer. The app is completely free on Connect IQ:
apps.garmin.com/.../d172e58d-c6f0-4ece-876b-8f39b0c8eb33
If you try it, device-specific feedback is very welcome.