We describe here results of a photometric time-sequence survey of the globular cluster M3 ( NGC 5272 ) , in a search for contact and detached eclipsing binary stars .
We have discovered only one likely eclipsing binary and one SX Phe type star in spite of monitoring 4077 stars with V < 20.0 and observing 25 BSS .
The newly identified SX Phe star , V237 , shows a light curve with a variable amplitude .
Variable V238 shows variability either with a period of 0.49 d or with a period of 0.25 d. On the cluster colour-magnitude diagram , the variable occupies a position a few hundredths of magnitude to the blue of the base of the red giant branch .
V238 is a likely descendent of a binary blue straggler .

As a side result we obtained high quality data for 42 of the previously known RR Lyrae variables , including 33 of Bailey type ab , 7 type c and 2 double-mode pulsators .
We used equations that relate the physical properties of RRc stars to their pulsation periods and Fourier parameters to derive masses , luminosities , temperatures and helium parameters for five of the RRc stars .
We also tested equations that relate [ Fe/H ] , M _ { V } and temperature of RRab stars to pulsation period and Fourier parameters .
We derived [ Fe/H ] = -1.42 in good agreement with spectroscopic determinations .
One of the RRd stars ( V79 ) has switched modes .
In previous studies , it was classified as RRab , but our observations show that it is an RRd star with the first overtone mode dominating .
This indicates blueward evolution on the horizontal branch .