Peak Flow chart

Please have a look at the attachment.

Enter your data in columns A, B and D - all the rest should be automatic

I've used data validation to ensure that only dates are entered in column A , AM/PM in B and a number in the allowable range in D.

An event driven macro will insert a formula in C to form a composite value for the data/time.

The data in columns C and D are described as named ranges which are used to drive the chart.

I've started the sheet off with some (pessimistic ) fake data for demonstration purposes.

Hope this helps.

I tried to load the file, but it says it contains errors, then when I try to close it, it freezes excel.

Try this version.