The letter o is normally easily recognisable but sometimes its formation, particularly in capital form, is made with a straight stroke making it harder to identify such as in the image below.
You can also find letter o written without forming a complete circle. This type of o is usually formed starting from the left hand side and working anti-clockwise.
When written tightly against a preceding letter, the letter o can cause difficulties. It is almost as if the letter has adhered to the preceeding letter, like a barnacle to the timbers of a ship. It happens most commonly with the letters, d, f, s and t though as with most things palaeographical a clerk's individual style can vary and you may find it occurs with other letters too.
In the word doe, below, it is hard to tell where the descending diagonal stroke of the d ends and where the letter o begins. As a result, it can look like a single letter, like a curly capital A.
In the word docate below, the letters d and o combine to look a bit like a snake, and, again, might make the unwary regard them as a single letter.
The most common problem with this tight o is in the word to. The example below shows five different versions of the word to. The first one is well formed and clearly written, the second and third less so and the last two look more like the number 6. This is because the cross-stroke of the t has been used as the beginning of the letter o. The biggest giveaway will be the context the word is in as the use of the word to can be fairly predictable.
In the examples below, this form of the word to, which looks like a number 6, occurs in the phrases spous to William and ordaned to amend. In the second example you can see in ordaned how the o is formed and thus how it becomes like a barnacle in to.
When sitting in close to an f the o can obscure the horizontal stroke of the f and make it easily confused with an s. The word below is fodder.