How will a capo work?

Most capo users have tuning problems. Every time you put the capo on or remove it you have to adjust the tuning. The capo eliminates the intonation fault in the nut! When these faults alternately are added and eliminated the tuning is affected. It's very tedious when artists turns their back to the audience to adjust the tuning.

Because "ordinary" (not intonated) instruments intonate bad both with and without capo, musicians often are careless when placing the capo. The placement doesn't matter that much - it sounds bad no matter what you do. But, If the instrument is intonated it is a pity to ruin it by incorrect placement of the capo.

A capo should always be placed as close to the fret as possible!

Careless placement of the capo adds extra clamping power to the string making its pitch too high. The main principal is that the strings should pass through the capo as straight as possible. By placing the capo as close to the fret as possible, the leverage of the capo is lessened and it becomes harder for the capo to bend the strings.
                     - A narrow capo bar shortens the lever.
                     - The contact area of the pad against the string should be flat.
                     - A distinct edge on the pad makes the placement easier.
Some capos have rounded pads - maybe to emulate a finger tip. Others have tubing around the bar and get a rounded contact area against the strings.

Strings fretted by the capo only intonates correctly. The capo frets the string just like a finger and as the instrument is intonated the note will be correct.

When the strings are fretted by both the capo and the fingers a small amount of pressure is added when the string is fretted in two places. Behind the finger the capo is pressing the string down the tiny little string height caused by the nut being somewhat higher than the frets. If the capo is correctly placed that little extra tension is hardly noticeable. You will not need to adjust the tuning when you use a capo!