Changing Text size based on a value in a dynamic block

[A1Caddman]

Hello

I have this dynamic block, (attached)

When the block variable d1 and d2 is a 10' or less I want the text height value for width and length to be .0001

and when the block variable of d1 or d2 is great than 10' it changes to be 18"

is this possible and if so can somebody point me in the right direction to achieve this

Thanks loads