Vehicle height error/glitch

Hi there,

I have a 7 inch wince 8gb sat nav running igo primo. It was advertised as a truck sat nav. When inputting the vehicle height it in particular doesn't seem to like the numbers 3,4,8,9. As it defaults to the number before it.

Example

I put in 3ft it defaults to 2ft
I put in 8ft it defaults 7ft
I put in 14ft it defaults to 13ft and so on.......

Is there anyway I can change this? please let me know if you need more information

Kind regards
QS

Perhaps the default enforces a constant safety margin of 1ft for the vehicle height and which it's not bad at all...