Data differs a lot

[rinfoh61]

Hi,

I need daily data to test and build trading systems. I am a small trader and can't really afford to buy data, especially since I want to test systems on a lot of different markets.

The problem is that the free data I have found differs a lot. I can't know what is right and what is wrong data and the systems I am testing show very different results depending on the data I use.

So, how can I know what data is true and what is shit?

 

[SplawnDarts]

What time frame of data and what instruments?

 

[rinfoh61]

What time frame of data and what instruments?

Daily data.

Interested in trying a lot of different instruments, in the long run; all of them.

Most interesting at the moment is: commodities, indexes and forex.