Recently, I got a "programmable cystal oscillator module" which can generate arbitral frequency signal from 1 MHz to 125 MHz. The output is generated by internal PLL, and it is commercial item and I think (believe) the accuracy is reliable and we will get any frequency with high accuracy. 

The above picture shows the measurement result of a clock module programmed as "3.1416 MHz". For hobby (and most of digital application) , these 5-digit accuracy

is enough but I don't have any confidence more than five digit. What happens less than more? In order to get what is the exact frequency of oscillation, we definitely need high precision frequency counter (or spectrum analyzer or else) driven by high precision frequency standard like rubidium oscillator. Even rubidium is not versatile due to its "aging". Periodic calibration is required to keep it and the price is not "inexpensive". Of course if you are involved in "national project", you can order and ask annual calibration but, at least, this is personal interest and I cannot pay hundreds dollars for it.. 

Indeed I was almost buying rubidium at eBay but actually really good news I found! u-blox's GPS module datasheet says it can generate arbitral frequency signal up to 10 MHz, which is SYNCHRONIZED to GPS time!!!!!!

Of course drives me to make high precision frequency counter trained by GPS signal!! Yeah!