1) Biliteral signs

Biliteral signs are signs that represent a combination of two consonants. The following list provides an overview of the most common signs.

Aw Ab iw im in ir is aA aq aD wA wa wp wn wn wr wD bA bH pA pr

pH mA mi mi mw mn mr mr mH ms mt m(w)t nw nw nb nm nn nH ns nD rw

HA Hw Hm Hn Hr Hs HD xA xa xw xt XA Xn Xn Xr sA sA sA sw sn sk

st st SA Sw Sn Ss Sd qd kA kp gm gs tA ti tm TA DA Dw Dr Dd

Some biliteral signs can also be used as ideograms. For instance, the sign can be used purely for its phonetic value in words such as   Hrj.t, "dread" and as an ideogram in the word , Hr, meaning "face". Note the use of the determinative stroke in the latter example to indicate that the sign (Hr) is to be interpreted as an ideogram. Also note that the reading of still is Hr and that the sign thus could also be viewed as being a phonogram.
In fact, the phonetic value of the sign can be explained as being derived from the word "face" that consists of the consonants H+r.

2) Phonetic complement

Biliteral signs are often combined with one or exceptionally two uniliteral signs that have the same phonetic value as one of the consonants of the biliteral sign. Uniliterals used in this way complement the reading of the biliteral signs and are called "phonetic complements". They are not read separately but are part of the phonetic value of the biliteral sign.
For instance, the biliteral sign is very often accompanied by the uniliteral , but the combination of these two signs is transcribed as mn and not as mnn. The added n only serves to complement the phonetic value of the biliteral sign .

In some cases, phonetic complements can help to distinguish between different values of the same sign. The sign , for instance, can be read as Ab or mr. The combination , however, must be read as Ab because the added b is a phonetic complement. Similarly, the combination is read mr because the added m and r are phonetic complements.

An additional benefit, at least for the modern-day reader, is that phonetic complements betray at least part of the reading of the signs they accompany.
It must, however, be noted that none of the biliteral signs actually needs to have phonetic complements. Thus the signs and , for instance, can be written with or without any phonetic complements. This can cause some ambiguity in reading and in text interpretation, particularly for a sign such as that has more than one reading.
One of the conjugated forms of the verb iri, "to do, to make" is irr, which can be written both as and as . In the latter case, the first r is a phonetic complement and the second r is part of the verb's conjugation. Another conjugated form of the same verb, however, is ir, which can be written as and as . The group can therefore be read as ir and as irr. Only a careful examination and a clear understanding of the context may help determining the intended reading.