The efficacy of orchestral tuning of instruments using one's ear with reference to the oboe, or digitally using a free mobile app such as Soundcorset, can be debated. However, to achieve greater tuning accuracy and in a much quicker fashion allowing each string to be tuned very accurately., the app wins out. The mobile app reference frequency can be set to 442 Hertz, a standard used by many leading leading orchestras, Another vg app is Total energy about 7 euros!