Isleham, then, was a normal ten-hide township, and confirms, instead of rebutting, the rule that the geldable hide contained 120 acres.[81] The remaining exceptions are 'Somm[er]tona' partly explained by the omission of _terra Regis_, 'Bathburgeham' (Babraham) with 21 acres short of an assessment of 7 hides, and Carlton, which fitly closes the list of these exceptions. For here, on an assessment of 10 hides, we have, according to the I.C.C., 27 acres short, but, according to D.B., 53-1/2 (27 + 20 + 6-1/2). A demonstrable blunder in Domesday Book and a discrepancy between it and the I.C.C. are responsible, together, for the difference.[82] Thus we see how wide a margin should be allowed, in these calculations, for textual error. It is necessary to remember that there were three processes, in each one of which error might arise: I. In the actual survey and its returns, 'by reason of the insignificance of some estates, or by reason of forgetfulness, or inaccuracy, or confusion, or doubt on the part of local jurors and witnesses, or of the clerks who indited their statements'.[83] II. In the collection and transmission of the returns, by the loss of a 'leaflet or rotulet of the commissioners' work'.[84] III. In the transcription of the returns into D.B., or into the I.C.C., _plus_, in the case of the former, the rearrangement and abridgment of the materials. We may now quit this part of our subject, claiming to have settled, by the aid of the I.C.C., a problem which has puzzled generations of antiquaries, namely: 'What was the Domesday hide?'[85] We have shown that it denoted a measure of assessment composed of four (geld) virgates or a hundred and twenty (geld) acres. What relation, if any, it bore to _area_ and to _value_ is a question wholly distinct, on which the next portion of this essay may throw quite a new light. VI. THE FIVE-HIDE UNIT It is one of the distinctive and valuable features of the _Inq. Com. Cant._ that it gives us the total assessment for each Vill of which it treats before recording the several Manors of which that Vill is composed, the aggregate assessments of which Manors make up the total assessment for the Vill. In this feature we have something which Domesday does not contain, and which (independently of its checking value),[86] gives us at once those Vill assessments which we could only extract from the Domesday entries by great labour and with much uncertainty. Let us see then if these Vill assessments lead us to any new conclusions on the whole assessment system.