Hello David,
Go by how you feel.
Other things you can do is take your temperature and your pulse.
It is best to take your temperature in the morning before you get out of bed. Have the thermometer ready when you go to bed (to use in the morning). Take your temp when you first wake, without having to get out of bed or move around too much.
The temperature is normally lower in the morning, but not much lower than 98.0
Hypothyroidism can cause the temp to be lower than it should. See what yours it; write it down and keep a record.
Take your pulse and keep a record of that too.
Are you splitting your dose and taking half in the morning and half later?
I feel so much better on Armour than I did on Synthroid. Hopefully it will help you too.