Geo Trio ii budget query

Staffordian11

Does anyone know the logic behind the calculations used for the budget display on the Geo Trio ii IHD?

I have set a budget of £71 per month, and have not selected the Seasonal budget adjustment. I reckon this should mean I can use up to between £2.29 and £2.53 per day (including standing charge) depending on how many days there are in the month and remain within budget.

But whenever I get to arould 4kWh in a day it says I am over budget. On my tariff, 4kWh is around £1.83 with the standing charge included.  As an example, today, I looked a moment ago and it said I had used 4.81kWh, at a cost of £2.12 (which is a couple of pence over by my calculation, but close enough) and the display showed red, and over budget (not predicted over budget).

The tariff details in the IHD menu are correct, at 33.73p per unit and 48.13p standing charge, and strangely, if I look at the weekly and monthly usage, both show that I am significantly under budget.

Can anyone explain this contradiction?

Thanks.