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 much greater tuning accuracy quickly, the app surely wins out? The mobile app reference frequency can be set to 442 Hertz, a standard used by many leading leading orchestras, allowing each string to be tuned very accurately. Another vg app is Total energy about 7 euros!