ever increasing numbers

after offsetting a line by 7mm, I needed to offset another line by 24mm. That command gave me a result of an offset of 724mm. Thinking I'd made an error, I attempted the 24mm offset again and the result was 72424mm. The number just keeps increasing for no apparent reason.

 

Does anyone know what setting I have accidently changed to have this happen?

 

Thanks

Frank