Sparklines Displaying Incorrectly

[evileconboy]

I've got some data (5% in each column, unvarying, for 10 years).

I constructed a spark line to cover this data, and Excel, for some reason, has the sparkline showing crazy variability. There is literally no variability in this data. It's 5% precisely. When I re-copy the formulas, the sparkline shows correctly (a straight line). But when I hit F9 to recalculate, the sparkline changes back to a squiggly line with crazy variability.

Clearly there is something about where the sparkline is getting its data that I don't understand. I've re-done the sparkline from scratch in other places, to no avail. Does anyone know what's going on that would make a sparkline pointing to constant data show variability?

 

[evileconboy]

I've actually found the answer here. Sparklines amplify small variances and compress large ones. I added a "round to 2 digits" on my figures and the spark lines compressed to show a flat line. I'm guessing that the floating point representation of numbers is hairy and has some weird side effect whereby large numbers divided to give a percentage look different from period to period, and the sparklines amplify that variation, even though those variations are infinitesimal.

 

[evileconboy]

here is a screenshot of the example. try it for yourself to see how this works