The rules of thumb that I use are derived from Fourier Analysis. You need to work out what frequencies are present, and then what their levels are.

1) The harmonics get less the higher you go, in proportion to "frequency to the power of n", where n is 1 for discontinuities in the voltage (like a square wave suddenly changing voltage), n is 2 for discontinuities in the voltage slope (like a triange wave, where the voltage doesn't change suddenly but the rate of change does), etc. up to a pure sine wave where there are no harmonics, n is "infinite" because the sine wave has a smooth waveform however many times you take the slope, the slope of the slope, etc.

So a square wave's harmonics are at the relative levels of

1/3, 1/5, 1/7, ... (no even harmonics, as explained below)

but a triangle wave has

1/(3^2), 1/(5^2), 1/(7^2)... = 1/9, 1/25, 1/49, ...

This kind of rule works better and better for higher frequencies. It works excellently for all frequencies with the simple examples here!

I've not said anything about the fundamental here. A rule of thumb eludes me at the moment...

2) You more often get odd harmonics, but the even harmonics are absent when the wave is the same backwards as upsidedown (I think the proper term is skew-symmetric).

This is a square wave, but you can't tell me whether I made it upsidedown or backwards:

| |-----| |-----| |-----| |-----| | | | | | | | | | | | | | | | | -> | | | | | | | | | | | | | | | | | | | | | | | | | |-----| |-----| | | |-----| |-----|

so it has no even harmonics. Same with a nice symmetrical triangle wave.

This one is not quite so square, having a duty cycle not 50%:

| |-----| |-----| |---| |---| | | | | | | | | | | | | | | | | -> | | | | | | | | | | | | | | | | | | | | | | | | | |---| |---| | | |-----| |-----|

and you can tell I turned it upsidedown, so it has even harmonics. Same with a saw-tooth wave.

So your example has a triangle wave at 1000Hz. I assume that it is symmetrical. OK? The frequencies present are the odd harmonics:

1000, 3000, 5000, 7000, ... You started with 100V of triangle wave. That has approx 80V of sine wave at 1000Hz, so
80V

* / 9 = 9V at 3000Hz
80V / *25 = 3V at 5000Hz etc

OK?!

Jean