Distance To Empty

It' a 13 year old car... That feature wasn't common in cars until about 10 years ago...

 

PriusCamper is correct. No DTE on Gen 2s.

 

DTE (AKA "Distance-to-Empty")=(A - (B / C)) x C= (A x C) - B

Assumptions:
A= gallons pumped at last fill-up (always fill-up when you fuel Prius)

B= miles driven since last fill-up (just reset "A" or "B" odometer to zero at fill-up)*

C= conservative fuel economy number in mpg

*- MFD automatically resets at fill-up but MFD mileage since fill-up is easier to accidentally reset.
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Example of Application of Above Formula (restated immediately below):
DTE = (A x C) - B

Hypothetical values (for use in this example):
A= 8 gallons pumped at last fill-up
B= 192 miles driven since last fill-up
C= 43mpg

Calculation of DTE:
DTE= =(8 gallons x 43mpg) -192 miles= 152 miles

PS I just noticed that OP is in Ireland. The above formula would work the same way with liters and km so long as mpg number is substituted with km/l (and fill-up amount is in liters and distance traveled is in km). Back of the envelope calc (IOW rough): 43mpg roughly equates to 18km/l.