Differing Magnetic Headings for three separate planning tools

[Dane]

I am just curious what causes three different navigation route plotting tools to be slightly different even though the routes are identical.

 

I recently noticed that the degrees calculated by SkyVector, Little NavMap, and AivlaSoft EFB2 are off by a couple degrees - some of the legs are the same while others differ.
Also note that for Little NavMap and AivlaSoft EFB2 I have both with AIRAC Cycle 1903, not sure what SkyVector uses or if this even matters.

 

Anyone have any thoughts on this phenomena?

See attached screenshots link of my plotted routes for: CZBB WC HUH KORS FHR BVS 3W5 

 

EDIT - Links

 

https://photos.app.goo.gl/SDwejagtdrFG962z5

https://photos.app.goo.gl/LtEhbYnqkiWtbWRR9

https://photos.app.goo.gl/JpD2Z6kqGZ5y79fs9

[lonewulf47]

Because no one source of magnetic variation is the same and can differ by quite some amount. Every state is allowed to use its own source and there is only an ICAO recommendation to update variation and station declination of navaids every year ending with -5 or -0 (zero). Every source can be used as long as it is shown somewhere on the map. GPS's and onboard navigation systems hold their own declination tables as do the various simulators. Furthermore e.g. LOC bearings are defined as magnetic bearings, recalculated to true bearings by using the magnetic variation noted in the respective state publication. You will always see a difference within different sources. No chance to overcome this unless the whole (real world) navigation is based on true bearings. Not sure when this will ever be introduced.

 

the good thing is: whatever navigation tool you use, you will always reach your destination, regardless whether variation is absolutely correct or not😀