Ok, I got an idea why there is difficulty.
1 step is to enter piston diameter (13.8 for example)
2 step is enter stroke (14.04 mm for example)
3 step is enter exhaust height ( 5 mm for example)
4 step is enter difference between exhaust height and transfer height (2 mm for example) Always when engine is designed, designer are interested in difference between exhaust and transfer-this is dictating pipe length. So from exhaust height needs to be subtracted transfer height.
5 step is pressing left bottom button, which says “calculate timings and capacity”

Second possibilities is reverse calculating:
If you know what timing you want to put, just put it and press right bottom button which says calculate exhaust and transfer height if timing known”
Please try this way, I hope it will help.