What can be the explanation for the check cif error " The unit-cell lengths a and c should be equal for a rhombohedral cell" ?

I have the following B level alerts in cif: Alert level B SYMMS02_ALERT_1_B The unit-cell lengths a and c should be equal for a rhombohedral cell Cell 8.1970 8.1970...

09 July 2021 6,267 0 View