Its possible that there are systematic error which I cant avoid so easly, for example, the object wasn't placed at zero distance correctly and thus this affects the measurement for V,U and F.

Its also possible that I made a mistake while reading the measurement from the ruler .From my point of view,I find that one of the most important mistakes that may I made is identifying the opject correctly in the right place and then replacing the ruler correctly without moving it and determining the appropriate position.Also It is assumed that the point of intersection of the curve with the x-axis(1/f2) is equal to its point of intersection with the y-axis(1/f1) but as you can see from my report there are not equal

It is possible to obtain a better and more correct result by taking measurements more accurately, replacing the correct numbers, and placing the ruler in the desired place accurately.Also its probable that the lens or the screen wasn't exactly perpendicular to the axis thus can effect my result.I also searched about this object and find that because I made the experiment not in the laboratory, we avoided many mistakes that could occur while making

it