Why are ammeters and oscilloscopes inaccurate for measuring small currents and voltages?

[dagg3r]

hi can somebody just breiefly list me some points about ammeters and how they are inaccurate and why when measuring in current in nano

and also about the cathode ray oscilloscope how when we plot voltages it is inaccurate and why.

thanks just basically want to know the limitations of these equipments

 

[hotvette]

This might help.

http://www.allaboutcircuits.com/vol_1/chpt_8/4.html