The angle of dangle

[katana]

Thank you for all the replies so far , often , it seems that 'definative' edge angles are described for knife sharpening and some for sword edges....but none seem to take into account of the type of steel/iron, edge hardness, blade profile etc. I wondered whether 'typical' and common ethno blades such as Kaskara, khanjar, Saifs, Kris etc had evolved with a 'traditional' optimum angle or that there was a range of several degrees and therefore less important.
It is sometimes very surprising how a few degrees of angle can greatly improve the cutting abillity of a blade. Is there any evidence that there is an ethnic belief in the 'perfect' angle ?

Kind Regards David