must descale
Regular verb: descale - descaled- descaled

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must descale
you must descale
he must descale
we must descale
you must descale
they must descale 	I must be descaling
you must be descaling
he must be descaling
we must be descaling
you must be descaling
they must be descaling	I must have descaled
you must have descaled
he must have descaled
we must have descaled
you must have descaled
they must have descaled	I must have been descaling
you must have been descaling
he must have been descaling
we must have been descaling
you must have been descaling
they must have been descaling	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must not descale
you must not descale
he must not descale
we must not descale
you must not descale
they must not descale 	I must not be descaling
you must not be descaling
he must not be descaling
we must not be descaling
you must not be descaling
they must not be descaling	I must not have descaled
you must not have descaled
he must not have descaled
we must not have descaled
you must not have descaled
they must not have descaled	I must not have been descaling
you must not have been descaling
he must not have been descaling
we must not have been descaling
you must not have been descaling
they must not have been descaling	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I descale?
must you descale?
must he descale?
must we descale?
must you descale?
must they descale? 	must I be descaling?
must you be descaling?
must he be descaling?
must we be descaling?
must you be descaling?
must they be descaling? 	must I have descaled?
must you have descaled?
must he have descaled?
must we have descaled?
must you have descaled?
must they have descaled? 	must I have been descaling?
must you have been descaling?
must he have been descaling?
must we have been descaling?
must you have been descaling?
must they have been descaling? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I not descale?
must you not descale?
must he not descale?
must we not descale?
must you not descale?
must they not descale? 	must I not be descaling?
must you not be descaling?
must he not be descaling?
must we not be descaling?
must you not be descaling?
must they not be descaling? 	must I not have descaled?
must you not have descaled?
must he not have descaled?
must we not have descaled?
must you not have descaled?
must they not have descaled? 	must I not have been descaling?
must you not have been descaling?
must he not have been descaling?
must we not have been descaling?
must you not have been descaling?
must they not have been descaling?