What Was the Accuracy of Macro Model in the Phillips' Machine (MONIAC)?
Phillips himself claims writing about Moniac like machines in 1950: &quot;The accuracy obtained depends on the precision with which the machines are constructed, but there is no difficulty keeping it within about $\pm$ 4%&quot; (p.284)
The article also points out that at the time of writing he was still building the MONIAC at LSE, but had already constructed one in Leeds. I suppose the LSE version turned out to be accurate upto 2%, and hence the conflicting informaton.
Economica, New Series, Vol. 17, No. 67. (Aug., 1950), pp. 283-305. Here's a link

Two unrelated fun-facts:
The MONIAC features in Terry Pratchett's Discworld novel: Making Money. As always in Pratchett's novels there are a lot of references to roundworld reality: introduction of paper money, outsourcing, inflation due to money dilution and many others
The Dutch have an expression &quot;To have money like water&quot; which in the Dutch context obviously means to have lots of money. The MONIAC is one of the few cases where it can be interpreted literally.