i had the same problem , the best thing to do is to press the up and down buttons together , keep them hold until the word CAL comes up , then press the up button until it gets to 99 , then press the across button , the word SET should come up , this should sort things out for you , then all you need to do is run the pump and find your flow rate , i use it on 75 with the blue fan jets from vari tech and 100 M of 6mm microbore .
Hope this helps
Rich P @ F