studio7conga wrote:what do you mean by 5-15 cnets sharp? is that not a "standard" C, for example? have you found a good digital tuner to use with congas?
thanks, 
studio7conga
I use an old Korg digital tuner.  It has a built in microphone but it works better with a quality mic plugged in the 1/4 inch jack.  I also use my son's Boss digital tuner in the same manner with an external mic.  The type of tuner to use is an auto-ranging tuner that will detect the value of the note automatically.  When reading the meter, 0 cents is perfect tune and the tuning range for "in tune" is +/- 5 cents.  The meter scale is in cents.  
I have built a 3 1/2 octave poplar wood marimba with 4" wide poplar keys (scrap from a construction site) with the Korg.  I also have found the sympathetic frequency of my congas with the Korg as well.  I have found that when I tune my congas to the shell's sympathetic frequency that I have the best tunings possible for the shell.  To find the sympathetic frequency, I detune the head or have the head removed and I thump the shell bottom on my hardwood floor.  After several tests, I find the average value of the shell's thumping.  A shell with C sympathetic frequency could be tuned to the Key of C and a relative Key with C.  The shell is best tuned to C, E, Eb, F, F#, G, A and B, the rest is upto the head.
When tuning with a digital meter, you will find that harmonics and relative notes will read out.  For example when tuning to C, I will read C, E and G but C will be the domanant value.  Tuning to D I often read D domanant but F# and A will flash as I approach D.  This is because the harmonics created by the drum and its tuning.  
Tuning in this manner, will allow you to play a set of congas that will create harmonics in addition to the notes played on the drums.  A set will be sympathetic to each other when tuned to the same key like D (A, D, F# & A).  If other drums are added to this that do not fit the key, then dissonance will take away from the over all sound.  Notes a 1/2 step and 1 step apart played at the same time will create dissonance (F and F# or A and B).  Ther needs to be an interval like a cord between the drums being played together for this to work out best.
In the end you let your ears decide what sounds best.