Working with a date column that corresponds to values in another column in SAS - sorting

Question

I would like to add on to this code so that the value of the last measurement according to the "date" column in the "measurement" column is divided by the lowest value recorded in the measurement column and the result forms a new column. The current working code adds a column that subtracts the initial measurements from the other measurements in the "measurement" column if the "subject", "type" and "procedure" columns match. Thank you in advance.
data have;
input Subject Type Date $ 5-12 Procedure $ 15-22 Measurement;
datalines;
500 Initial 15 AUG 2017 Invasive 20
500 Initial 18 SEPT 2018 Surface 35
500 Followup 12 SEPT 2018 Invasive 54
428 Followup 2 JUL 2019 Outer 29
765 Seventh 3 JUL 2018 Other 13
500 Followup 6 NOV 2018 Surface 98
428 Initial 23 FEB 2018 Outer 10
765 Initial 20 AUG 2019 Other 19
610 Third 21 AUG 2018 Invasive 66
610 Initial 27 Mar 2018 Invasive 17
;
data want (drop=rc _Measurement);
if _N_ = 1 then do;
declare hash h (dataset : "have (rename=(Measurement=_Measurement) where=(Type='Initial'))");
h.definekey ('Subject');
h.definedata ('_Measurement');
h.definedone();
end;
set have;
_Measurement=.;
if Type ne 'Initial' then rc = h.find();
NewMeasurement = ifn(Measurement=., ., sum (Measurement, -_Measurement));
run;