I have some ceramic capacitors which I can identify (all are brown):
on several is 10 with an underline and nothing else
on another is 103 underlined
and 221 underlined
have been searching for any information about the underline and come up dry.
Thanks much..
Normally, "10" would be 10 pf, "103" would be 10,000 pf (i.e. "10" followed by 3 zeroes), and "221" would be 220 pf ("22" followed by 1 zero).
But let's see what others say...
If the number is 1 or 2 digits it is the capacitor value in pF. If the number is 3 digits the third digit is the power of ten exponent by which the first 2 digits are multiplied to get the value in pF.
Thanks to both!
So the 221 is 220pF NOT 22pF - glad I asked - I thought the 3rd number might mean to multiply the first 2 digits by 1 which would equal 22pF.
But just a 22 would mean just that, 22pF.
sorry to ask such basic questions but I'm in the boonies and it takes days if not weeks to get parts here so looking through stuff.
Neither of you said anything about the underline -- is it just to show the baseline of the numbers, i.e., so a 9 is shown as a 9 and not confused with a 6?
Correct... 2 digits by themselves are in pF, so yes, 22 or 10 would be 22pF and 10pF.
Caps in nF format tend to actually say nF Example: 0.1uF polyester cap could be marked 100nF and would be clearly marked that way with at least an "n" showing.
Strangely the manufacturers of capacitors aren't keen about new-fangled nano- or milli- prefixes, and took long
enough to switch from micro-micro-farads to pico-farads!
Its very common to see awful values like 0.001uF, 47,000uF or 220,000pF being bandied about rather than
1nF, 47mF and 220nF - whereas the manufacturer's of inductors are quite happy to use nH, uH, mH in a
grown-up way. Always wondered why this was...
In the case of 47,000 µF, it is clearly because that sounds more impressive than 47 mF. 
Thanks all -- very much -- for a beginner capacitors are a real rat's nest.
I did find a beginner-friendly article here:
https://learn.sparkfun.com/tutorials/capacitors
A good basic intro, thought the caption on the image for ceramic capacitors is thoroughly confusing!
Cheers,
Clair